Microorganisms and methods for the biosynthesis of propylene

ABSTRACT

The invention provides non-naturally occurring microbial organisms having a propylene pathway. The invention additionally provides methods of using such organisms to produce propylene.

This application claims the benefit of priority of U.S. Provisional application Ser. No. 61/330,258, filed Apr. 30, 2010, the entire contents of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to biosynthetic processes, and more specifically to organisms having propylene biosynthetic capability.

Propylene is produced primarily as a by-product of petroleum refining and of ethylene production by steam cracking of hydrocarbon feedstocks. Propene is separated by fractional distillation from hydrocarbon mixtures obtained from cracking and other refining processes. Typical hydrocarbon feedstocks are from non-renewable fossil fuels, such as petroleum, natural gas and to a much lesser extent coal. Over 75 billion pounds of propylene are manufactured annually, making it the second largest fossil-based chemical produced behind ethylene. Propylene is a base chemical that is converted into a wide range of polymers, polymer intermediates and chemicals. Some of the most common derivatives of chemical and polymer grade propylene are polypropylene, acrylic acid, butanol, butanediol, acrylonitrile, propylene oxide, isopropanol and cumene. The use of the propylene derivative, polypropylene, in the production of plastics, such as injection moulding, and fibers, such as carpets, accounts for over one-third of U.S. consumption for this derivative. Propylene is also used in the production of synthetic rubber and as a propellant or component in aerosols.

The ability to manufacture propylene from alternative and/or renewable feedstocks would represent a major advance in the quest for more sustainable chemical production processes. One possible way to produce propylene renewably involves fermentation of sugars or other feedstocks to produce the alcohols 2-propanol (isopropanol) or 1-propanol, which is separated, purified, and then dehydrated to propylene in a second step involving metal-based catalysis. Direct fermentative production of propylene from renewable feedstocks would obviate the need for dehydration. During fermentative production, propylene gas would be continuously emitted from the fermenter, which could be readily collected and condensed. Developing a fermentative production process would also eliminate the need for fossil-based propylene and would allow substantial savings in cost, energy, and harmful waste and emissions relative to petrochemically-derived propylene.

Microbial organisms and methods for effectively producing propylene from cheap renewable feedstocks such as molasses, sugar cane juice, and sugars derived from biomass sources, including agricultural and wood waste, as well as C1 feedstocks such as syngas and carbon dioxide, are described herein and include related advantages.

SUMMARY OF THE INVENTION

The invention provides non-naturally occurring microbial organisms containing propylene pathways comprising at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce propylene. The invention additionally provides methods of using such microbial organisms to produce propylene, by culturing a non-naturally occurring microbial organism containing propylene pathways as described herein under conditions and for a sufficient period of time to produce propylene.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the conversion of 2-ketoglutarate to ethylene and carbon dioxide by an ethylene forming enzyme.

FIG. 2 shows an exemplary pathway for production of propylene from 2-ketoglutarate by a 2-ketoglutarate methyltransferase and a propylene forming enzyme.

FIG. 3 shows exemplary pathways for production of propylene from pyruvate. Enzymes for transformation of the identified substrates to products include: A) a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, B) a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase II, C) a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase I, D) a 4-methylene-2-ketoglutarate reductase, E) a 4-methyl-2-ketoglutaconate reductase, and F) a propylene forming enzyme.

FIG. 4 shows pathways from leucine and acetoacetate to 3-methyl-2-ketoglutarate. Enzymes for transformation of the identified substrates to products include: A. Leucine aminotransferase, dehydrogenase (deaminating) or oxidase, B. 4-methyl-2-oxopentanoate dehydrogenase, C. isovaleryl-CoA dehydrogenase, D. 3-methylcrotonyl-CoA carboxylase, E. 3-methylglutaconyl-CoA hydrolase, transferase or synthetase, F. 3-methylglutaconate hydratase, G. 3-methyl-2-hydroxyglutarate dehydrogenase, H. 3-hydroxy-3-methylglutaryl-CoA dehydratase and I. 3-hydroxy-3-methylglutaryl-CoA lyase.

FIG. 5 shows pathways to 4-methyl-2-oxoglutarate from lysine. Enzymes for transformation of the identified substrates to products include: A. Lysine 6-aminotransferase, 6-dehydrogenase (deaminating) or 6-oxidase, B. 2-aminoadipate dehydrogenase, C. 2-aminoadipate mutase, D. 4-methyl-2-aminoglutarate aminotransferase, dehydrogenase (deaminating) or oxidase, E. 2-aminoadipate aminotransferase, dehydrogenase (deaminating) or oxidase, and F. 2-oxoadipate mutase.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to the design and production of cells and organisms having biosynthetic production capabilities for propylene. The invention, in particular, relates to the design of microbial organism capable of producing propylene by introducing one or more nucleic acids encoding a propylene pathway enzyme.

In one embodiment, the invention utilizes in silico stoichiometric models of Escherichia coli metabolism that identify metabolic designs for biosynthetic production of propylene. The results described herein indicate that metabolic pathways can be designed and recombinantly engineered to achieve the biosynthesis of propylene in Escherichia coli and other cells or organisms. Biosynthetic production of propylene, for example, for the in silico designs can be confirmed by construction of strains having the designed metabolic genotype. These metabolically engineered cells or organisms also can be subjected to adaptive evolution to further augment propylene biosynthesis, including under conditions approaching theoretical maximum growth.

In certain embodiments, the propylene biosynthesis characteristics of the designed strains make them genetically stable and particularly useful in continuous bioprocesses. Separate strain design strategies were identified with incorporation of different non-native or heterologous reaction capabilities into E. coli or other host organisms leading to propylene producing metabolic pathways from either 2-ketoglutarate or pyruvate. In silico metabolic designs were identified that resulted in the biosynthesis of propylene in microorganisms from each of these substrates or metabolic intermediates.

Strains identified via the computational component of the platform can be put into actual production by genetically engineering any of the predicted metabolic alterations, which lead to the biosynthetic production of propylene or other intermediate and/or downstream products. In yet a further embodiment, strains exhibiting biosynthetic production of these compounds can be further subjected to adaptive evolution to further augment product biosynthesis. The levels of product biosynthesis yield following adaptive evolution also can be predicted by the computational component of the system.

The maximum theoretical propylene yield from glucose is 1.33 mol/mol (0.311 g/g):

3C₆H₁₂O₆=4C₃H₆+6CO₂+6H₂O

The pathways presented in FIGS. 2 and 3 achieve a yield of 1 mole propylene per mole of glucose utilized assuming 2 pyruvate molecules or 1 alpha-ketoglutarate molecule can be formed from glucose. Increasing product yields to 1.33 mol/mol is possible if cells are capable of fixing some of the CO₂ released from the depicted pathways or from the production of alpha-ketoglutarate through carbon-fixing mechanisms such as the reductive (or reverse) TCA cycle or the Wood-Ljungdahl pathway supplemented with pyruvate:ferredoxin oxidoreductase.

As used herein, the term “non-naturally occurring” when used in reference to a microbial organism or microorganism of the invention is intended to mean that the microbial organism has at least one genetic alteration not normally found in a naturally occurring strain of the referenced species, including wild-type strains of the referenced species. Genetic alterations include, for example, modifications introducing expressible nucleic acids encoding metabolic polypeptides, other nucleic acid additions, nucleic acid deletions and/or other functional disruption of the microbial organism's genetic material. Such modifications include, for example, coding regions and functional fragments thereof, for heterologous, homologous or both heterologous and homologous polypeptides for the referenced species. Additional modifications include, for example, non-coding regulatory regions in which the modifications alter expression of a gene or operon. Exemplary metabolic polypeptides include enzymes or proteins within a propylene biosynthetic pathway.

A metabolic modification refers to a biochemical reaction that is altered from its naturally occurring state. Therefore, non-naturally occurring microorganisms can have genetic modifications to nucleic acids encoding metabolic polypeptides, or functional fragments thereof. Exemplary metabolic modifications are disclosed herein.

As used herein, the term “propylene,” having the molecular formula C₃H₆ and a molecular mass of 42.08 g/mol (see FIGS. 2 and 3) (IUPAC name Propene) is used interchangeably throughout with 1-propene, 1-propylene, methylethene and methylethylene. At room temperature, propylene is a colorless gas with a weak but unpleasant smell. Propylene has a higher density and boiling point than ethylene due to its greater size, whereas it has a slightly lower boiling point than propane in addition to being more volatile. Propylene lacks strongly polar bonds, yet the molecule has a small dipole moment due to its reduced symmetry. Propylene is also a structural isomer to cyclopropane.

As used herein, the term “isolated” when used in reference to a microbial organism is intended to mean an organism that is substantially free of at least one component as the referenced microbial organism is found in nature. The term includes a microbial organism that is removed from some or all components as it is found in its natural environment. The term also includes a microbial organism that is removed from some or all components as the microbial organism is found in non-naturally occurring environments. Therefore, an isolated microbial organism is partly or completely separated from other substances as it is found in nature or as it is grown, stored or subsisted in non-naturally occurring environments. Specific examples of isolated microbial organisms include partially pure microbes, substantially pure microbes and microbes cultured in a medium that is non-naturally occurring.

As used herein, the terms “microbial,” “microbial organism” or “microorganism” are intended to mean any organism that exists as a microscopic cell that is included within the domains of archaea, bacteria or eukarya. Therefore, the term is intended to encompass prokaryotic or eukaryotic cells or organisms having a microscopic size and includes bacteria, archaea and eubacteria of all species as well as eukaryotic microorganisms such as yeast and fungi. The term also includes cell cultures of any species that can be cultured for the production of a biochemical.

As used herein, the term “S-Adenosyl methionine” or “SAM,” having the molecular formula C₁₅H₂₂N₆O₅S⁺ and a molecular mass of 398.44 g/mol (IUPAC name: (2S)-2-Amino-4-[[(2S,3S,4R,5R)-5-(6-aminopurin-9-yl)-3,4-dihydroxyoxolan-2-yl]methyl-methylsulfonio]butanoate) is a co-substrate involved in methyl group transfers. Transmethylation, transsulfuration, and aminopropylation are some of the metabolic pathways that use SAM. The methyl group (CH₃) attached to the methionine sulfur atom in SAM is chemically reactive. This allows donation of this group to an acceptor substrate in transmethylation reactions.

As used herein, the term “CoA” or “coenzyme A” is intended to mean an organic cofactor or prosthetic group (nonprotein portion of an enzyme) whose presence is required for the activity of many enzymes (the apoenzyme) to form an active enzyme system. Coenzyme A functions in certain condensing enzymes, acts in acetyl or other acyl group transfer and in fatty acid synthesis and oxidation, pyruvate oxidation and in other acetylation.

As used herein, the term “substantially anaerobic” when used in reference to a culture or growth condition is intended to mean that the amount of oxygen is less than about 10% of saturation for dissolved oxygen in liquid media. The term also is intended to include sealed chambers of liquid or solid medium maintained with an atmosphere of less than about 1% oxygen.

“Exogenous” as it is used herein is intended to mean that the referenced molecule or the referenced activity is introduced into the host microbial organism. The molecule can be introduced, for example, by introduction of an encoding nucleic acid into the host genetic material such as by integration into a host chromosome or as non-chromosomal genetic material such as a plasmid. Therefore, the term as it is used in reference to expression of an encoding nucleic acid refers to introduction of the encoding nucleic acid in an expressible form into the microbial organism. When used in reference to a biosynthetic activity, the term refers to an activity that is introduced into the host reference organism. The source can be, for example, a homologous or heterologous encoding nucleic acid that expresses the referenced activity following introduction into the host microbial organism. Therefore, the term “endogenous” refers to a referenced molecule or activity that is present in the host. Similarly, the term when used in reference to expression of an encoding nucleic acid refers to expression of an encoding nucleic acid contained within the microbial organism. The term “heterologous” refers to a molecule or activity derived from a source other than the referenced species whereas “homologous” refers to a molecule or activity derived from the host microbial organism. Accordingly, exogenous expression of an encoding nucleic acid of the invention can utilize either or both a heterologous or homologous encoding nucleic acid.

It is understood that when more than one exogenous nucleic acid is included in a microbial organism that the more than one exogenous nucleic acids refers to the referenced encoding nucleic acid or biosynthetic activity, as discussed above. It is further understood, as disclosed herein, that such more than one exogenous nucleic acids can be introduced into the host microbial organism on separate nucleic acid molecules, on polycistronic nucleic acid molecules, or a combination thereof, and still be considered as more than one exogenous nucleic acid. For example, as disclosed herein a microbial organism can be engineered to express two or more exogenous nucleic acids encoding a desired pathway enzyme or protein. In the case where two exogenous nucleic acids encoding a desired activity are introduced into a host microbial organism, it is understood that the two exogenous nucleic acids can be introduced as a single nucleic acid, for example, on a single plasmid, on separate plasmids, can be integrated into the host chromosome at a single site or multiple sites, and still be considered as two exogenous nucleic acids. Similarly, it is understood that more than two exogenous nucleic acids can be introduced into a host organism in any desired combination, for example, on a single plasmid, on separate plasmids, can be integrated into the host chromosome at a single site or multiple sites, and still be considered as two or more exogenous nucleic acids, for example three exogenous nucleic acids. Thus, the number of referenced exogenous nucleic acids or biosynthetic activities refers to the number of encoding nucleic acids or the number of biosynthetic activities, not the number of separate nucleic acids introduced into the host organism.

The non-naturally occurring microbal organisms of the invention can contain stable genetic alterations, which refers to microorganisms that can be cultured for greater than five generations without loss of the alteration. Generally, stable genetic alterations include modifications that persist greater than 10 generations, particularly stable modifications will persist more than about 25 generations, and more particularly, stable genetic modifications will be greater than 50 generations, including indefinitely.

Those skilled in the art will understand that the genetic alterations, including metabolic modifications exemplified herein, are described with reference to a suitable host organism such as E. coli and their corresponding metabolic reactions or a suitable source organism for desired genetic material such as genes for a desired metabolic pathway. However, given the complete genome sequencing of a wide variety of organisms and the high level of skill in the area of genomics, those skilled in the art will readily be able to apply the teachings and guidance provided herein to essentially all other organisms. For example, the E. coli metabolic alterations exemplified herein can readily be applied to other species by incorporating the same or analogous encoding nucleic acid from species other than the referenced species. Such genetic alterations include, for example, genetic alterations of species homologs, in general, and in particular, orthologs, paralogs or nonorthologous gene displacements.

An ortholog is a gene or genes that are related by vertical descent and are responsible for substantially the same or identical functions in different organisms. For example, mouse epoxide hydrolase and human epoxide hydrolase can be considered orthologs for the biological function of hydrolysis of epoxides. Genes are related by vertical descent when, for example, they share sequence similarity of sufficient amount to indicate they are homologous, or related by evolution from a common ancestor. Genes can also be considered orthologs if they share three-dimensional structure but not necessarily sequence similarity, of a sufficient amount to indicate that they have evolved from a common ancestor to the extent that the primary sequence similarity is not identifiable. Genes that are orthologous can encode proteins with sequence similarity of about 25% to 100% amino acid sequence identity. Genes encoding proteins sharing an amino acid similarity less that 25% can also be considered to have arisen by vertical descent if their three-dimensional structure also shows similarities. Members of the serine protease family of enzymes, including tissue plasminogen activator and elastase, are considered to have arisen by vertical descent from a common ancestor.

Orthologs include genes or their encoded gene products that through, for example, evolution, have diverged in structure or overall activity. For example, where one species encodes a gene product exhibiting two functions and where such functions have been separated into distinct genes in a second species, the three genes and their corresponding products are considered to be orthologs. For the production of a biochemical product, those skilled in the art will understand that the orthologous gene harboring the metabolic activity to be introduced or disrupted is to be chosen for construction of the non-naturally occurring microorganism. An example of orthologs exhibiting separable activities is where distinct activities have been separated into distinct gene products between two or more species or within a single species. A specific example is the separation of elastase proteolysis and plasminogen proteolysis, two types of serine protease activity, into distinct molecules as plasminogen activator and elastase. A second example is the separation of mycoplasma 5′-3′ exonuclease and Drosophila DNA polymerase III activity. The DNA polymerase from the first species can be considered an ortholog to either or both of the exonuclease or the polymerase from the second species and vice versa.

In contrast, paralogs are homologs related by, for example, duplication followed by evolutionary divergence and have similar or common, but not identical functions. Paralogs can originate or derive from, for example, the same species or from a different species. For example, microsomal epoxide hydrolase (epoxide hydrolase I) and soluble epoxide hydrolase (epoxide hydrolase II) can be considered paralogs because they represent two distinct enzymes, co-evolved from a common ancestor, that catalyze distinct reactions and have distinct functions in the same species. Paralogs are proteins from the same species with significant sequence similarity to each other suggesting that they are homologous, or related through co-evolution from a common ancestor. Groups of paralogous protein families include HipA homologs, luciferase genes, peptidases, and others.

A nonorthologous gene displacement is a nonorthologous gene from one species that can substitute for a referenced gene function in a different species. Substitution includes, for example, being able to perform substantially the same or a similar function in the species of origin compared to the referenced function in the different species. Although generally, a nonorthologous gene displacement will be identifiable as structurally related to a known gene encoding the referenced function, less structurally related but functionally similar genes and their corresponding gene products nevertheless will still fall within the meaning of the term as it is used herein. Functional similarity requires, for example, at least some structural similarity in the active site or binding region of a nonorthologous gene product compared to a gene encoding the function sought to be substituted. Therefore, a nonorthologous gene includes, for example, a paralog or an unrelated gene.

Therefore, in identifying and constructing the non-naturally occurring microbial organisms of the invention having propylene biosynthetic capability, those skilled in the art will understand with applying the teaching and guidance provided herein to a particular species that the identification of metabolic modifications can include identification and inclusion or inactivation of orthologs. To the extent that paralogs and/or nonorthologous gene displacements are present in the referenced microorganism that encode an enzyme catalyzing a similar or substantially similar metabolic reaction, those skilled in the art also can utilize these evolutionally related genes.

Orthologs, paralogs and nonorthologous gene displacements can be determined by methods well known to those skilled in the art. For example, inspection of nucleic acid or amino acid sequences for two polypeptides will reveal sequence identity and similarities between the compared sequences. Based on such similarities, one skilled in the art can determine if the similarity is sufficiently high to indicate the proteins are related through evolution from a common ancestor. Algorithms well known to those skilled in the art, such as Align, BLAST, Clustal W and others compare and determine a raw sequence similarity or identity, and also determine the presence or significance of gaps in the sequence which can be assigned a weight or score. Such algorithms also are known in the art and are similarly applicable for determining nucleotide sequence similarity or identity. Parameters for sufficient similarity to determine relatedness are computed based on well known methods for calculating statistical similarity, or the chance of finding a similar match in a random polypeptide, and the significance of the match determined. A computer comparison of two or more sequences can, if desired, also be optimized visually by those skilled in the art. Related gene products or proteins can be expected to have a high similarity, for example, 25% to 100% sequence identity. Proteins that are unrelated can have an identity which is essentially the same as would be expected to occur by chance, if a database of sufficient size is scanned (about 5%). Sequences between 5% and 24% may or may not represent sufficient homology to conclude that the compared sequences are related. Additional statistical analysis to determine the significance of such matches given the size of the data set can be carried out to determine the relevance of these sequences.

Exemplary parameters for determining relatedness of two or more sequences using the BLAST algorithm, for example, can be as set forth below. Briefly, amino acid sequence alignments can be performed using BLASTP version 2.0.8 (Jan.-5-1999) and the following parameters: Matrix: 0 BLOSUM62; gap open: 11; gap extension: 1; x_dropoff: 50; expect: 10.0; wordsize: 3; filter: on. Nucleic acid sequence alignments can be performed using BLASTN version 2.0.6 (Sep.-16-1998) and the following parameters: Match: 1; mismatch: -2; gap open: 5; gap extension: 2; x_dropoff: 50; expect: 10.0; wordsize: 11; filter: off. Those skilled in the art will know what modifications can be made to the above parameters to either increase or decrease the stringency of the comparison, for example, and determine the relatedness of two or more sequences.

In some embodiments, the invention provides a non-naturally occurring microbial organism, including a microbial organism having a propylene pathway having at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce propylene, the propylene pathway including a 2-ketoglutarate methyltransferase or a propylene forming enzyme (see FIG. 2, steps 1-2). In one aspect, the non-naturally occurring microbial organism includes a microbial organism having a propylene pathway having at least one exogenous nucleic acid encoding propylene pathway enzymes expressed in a sufficient amount to produce propylene, the propylene pathway including a 2-ketoglutarate methyltransferase and a propylene forming enzyme (see FIG. 2, steps 1 and 2).

In some embodiments, the invention provides a non-naturally occurring microbial organism, including a microbial organism having a propylene pathway having at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce propylene, the propylene pathway including a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase II, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase I, a 4-methylene-2-ketoglutarate reductase, a 4-methyl-2-ketoglutaconate reductase or a propylene forming enzyme (see FIG. 3, steps A-F). In one aspect, the non-naturally occurring microbial organism includes a microbial organism having a propylene pathway having at least one exogenous nucleic acid encoding propylene pathway enzymes expressed in a sufficient amount to produce propylene, the propylene pathway including a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase II, a 4-methylene-2-ketoglutarate reductase and a propylene forming enzyme (see FIG. 3, steps A, B, C and F). In one aspect, the non-naturally occurring microbial organism includes a microbial organism having a propylene pathway having at least one exogenous nucleic acid encoding propylene pathway enzymes expressed in a sufficient amount to produce propylene, the propylene pathway including a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase I, a 4-methyl-2-ketoglutaconate reductase and a propylene forming enzyme (see FIG. 3, steps A, D, E and F).

In some embodiments, the invention provides a non-naturally occurring microbial organism, including a microbial organism having a propylene pathway having at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce propylene, the propylene pathway including a leucine aminotransferase, dehydrogenase (deaminating) or oxidase; a 4-methyl-2-oxopentanoate dehydrogenase; an isovaleryl-CoA dehydrogenase; a 3-methylcrotonyl-CoA carboxylase; a 3-methylglutaconyl-CoA hydrolase, transferase or synthetase; a 3-methylglutaconate hydratase; a 3-methyl-2-hydroxyglutarate dehydrogenase; a 3-hydroxy-3-methylglutaryl-CoA dehydratase; or a 3-hydroxy-3-methylglutaryl-CoA lyase (see FIG. 4, steps A-I). In one aspect, the non-naturally occurring microbial organism includes a microbial organism having a propylene pathway having at least one exogenous nucleic acid encoding propylene pathway enzymes expressed in a sufficient amount to produce propylene, the propylene pathway including a leucine aminotransferase, dehydrogenase (deaminating) or oxidase; a 4-methyl-2-oxopentanoate dehydrogenase; a isovaleryl-CoA dehydrogenase; a 3-methylcrotonyl-CoA carboxylase; a 3-methylglutaconyl-CoA hydrolase, transferase or synthetase; a 3-methylglutaconate hydratase; a 3-methyl-2-hydroxyglutarate dehydrogenase and a propylene forming enzyme (see FIG. 4, steps A-G and FIG. 2, step 2). In one aspect, the non-naturally occurring microbial organism includes a microbial organism having a propylene pathway having at least one exogenous nucleic acid encoding propylene pathway enzymes expressed in a sufficient amount to produce propylene, the propylene pathway including a 3-methylglutaconyl-CoA hydrolase, transferase or synthetase; a 3-methylglutaconate hydratase; a 3-methyl-2-hydroxyglutarate dehydrogenase; a 3-hydroxy-3-methylglutaryl-CoA dehydratase; a 3-hydroxy-3-methylglutaryl-CoA lyase and a propylene forming enzyme (see FIG. 4, steps I, H, E-G and FIG. 2, step 2). Sources of encoding nucleic acids for a propylene pathway enzyme or protein described above are well known in the art and can be obtained from a variety of species including, but limited to, those exemplified herein.

In some embodiments, the invention provides a non-naturally occurring microbial organism, including a microbial organism having a propylene pathway having at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce propylene, the propylene pathway including a lysine 6-aminotransferase, a 6-dehydrogenase (deaminating) or 6-oxidase; an 2-aminoadipate dehydrogenase; an 2-aminoadipate mutase; a 4-methyl-2-aminoglutarate aminotransferase, dehydrogenase (deaminating) or oxidase; a 2-aminoadipate aminotransferase, dehydrogenase (deaminating) or oxidase; or a 2-oxoadipate mutase (see FIG. 5, steps A-F). In one aspect, the non-naturally occurring microbial organism includes a microbial organism having a propylene pathway having at least one exogenous nucleic acid encoding propylene pathway enzymes expressed in a sufficient amount to produce propylene, the propylene pathway including a lysine 6-aminotransferase, 6-dehydrogenase (deaminating) or 6-oxidase; an 2-aminoadipate dehydrogenase, an 2-aminoadipate mutase; a 4-methyl-2-aminoglutarate aminotransferase, dehydrogenase (deaminating) or oxidase; and a propylene forming enzyme (see FIG. 5, steps A-D, FIG. 3, step F). In one aspect, the non-naturally occurring microbial organism includes a microbial organism having a propylene pathway having at least one exogenous nucleic acid encoding propylene pathway enzymes expressed in a sufficient amount to produce propylene, the propylene pathway including a lysine 6-aminotransferase, 6-dehydrogenase (deaminating) or 6-oxidase; a 2-aminoadipate dehydrogenase; an 2-aminoadipate aminotransferase, dehydrogenase (deaminating) or oxidase; an 2-oxoadipate mutase; and a propylene forming enzyme (see FIG. 5, steps A, B, E and F, FIG. 3, step F). Sources of encoding nucleic acids for a propylene pathway enzyme or protein described above are well known in the art and can be obtained from a variety of species including, but limited to, those exemplified herein.

In an additional embodiment, the invention provides a non-naturally occurring microbial organism having a propylene pathway, wherein the non-naturally occurring microbial organism comprises at least one exogenous nucleic acid encoding an enzyme or protein that converts a substrate to a product selected from the group consisting of 2-ketoglutarate to 3-methyl-2-ketoglutarate, 3-methyl-2-ketoglutarate to propylene, pyruvate to 4-hydroxy-4-methyl-2-ketoglutarate, 4-hydroxy-4-methyl-2-ketoglutarate to 4-methylene-2-ketoglutarate, 4-methylene-2-ketoglutarate to 4-methyl-2-ketoglutarate, 4-hydroxy-4-methyl-2-ketoglutarate to 4-methyl-2-ketoglutaconate, 4-methyl-2-ketoglutaconate to 4-methyl-2-ketoglutarate or 4-methyl-2-ketoglutarate to propylene. One skilled in the art will understand that these are merely exemplary and that any of the substrate-product pairs disclosed herein suitable to produce a desired product and for which an appropriate activity is available for the conversion of the substrate to the product can be readily determined by one skilled in the art based on the teachings herein. Thus, the invention provides a non-naturally occurring microbial organism containing at least one exogenous nucleic acid encoding an enzyme or protein, where the enzyme or protein converts the substrates and products of a propylene pathway, such as that shown in FIGS. 2-5.

While generally described herein as a microbial organism that contains a propylene pathway, it is understood that the invention additionally provides a non-naturally occurring microbial organism comprising at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce an intermediate of a propylene pathway. For example, as disclosed herein, a propylene pathway is exemplified in FIGS. 2-5. Therefore, in addition to a microbial organism containing a propylene pathway that produces propylene, the invention additionally provides a non-naturally occurring microbial organism comprising at least one exogenous nucleic acid encoding a propylene pathway enzyme, where the microbial organism produces a propylene pathway intermediate, for example, 3-methyle-ketoglutarate, 4-hydroxy-4-methyl-2-ketoglutarate, 4-methylene-2-ketoglutarate, 4-methyl-2-ketoglutaconate, or 4-methyl-2-ketoglutarate.

It is understood that any of the pathways disclosed herein, as described in the Examples and exemplified in the Figures, including the pathways of FIGS. 2-5, can be utilized to generate a non-naturally occurring microbial organism that produces any pathway intermediate or product, as desired. As disclosed herein, such a microbial organism that produces an intermediate can be used in combination with another microbial organism expressing downstream pathway enzymes to produce a desired product. However, it is understood that a non-naturally occurring microbial organism that produces a propylene pathway intermediate can be utilized to produce the intermediate as a desired product.

The invention is described herein with general reference to the metabolic reaction, reactant or product thereof, or with specific reference to one or more nucleic acids or genes encoding an enzyme associated with or catalyzing, or a protein associated with, the referenced metabolic reaction, reactant or product. Unless otherwise expressly stated herein, those skilled in the art will understand that reference to a reaction also constitutes reference to the reactants and products of the reaction. Similarly, unless otherwise expressly stated herein, reference to a reactant or product also references the reaction, and reference to any of these metabolic constituents also references the gene or genes encoding the enzymes that catalyze or proteins involved in the referenced reaction, reactant or product. Likewise, given the well known fields of metabolic biochemistry, enzymology and genomics, reference herein to a gene or encoding nucleic acid also constitutes a reference to the corresponding encoded enzyme and the reaction it catalyzes or a protein associated with the reaction as well as the reactants and products of the reaction.

As disclosed herein, the intermediates 3-methyl-2-ketoglutarate, 4-hydroxy-4-methyl-2-ketoglutarate, 4-methyl-2-ketoglutaconate, 4-methylene-2-ketoglutarate, 4-methyl-2-ketoglutarate, 4-methyl-2-oxopentanoate, 3-methylglutaconate, 3-methyl-2-hydroxyglutarate, 2-aminoadipate semialdehyde, 2-aminoadipate, 2-oxoadipate, and 4-methyl-2-aminoglutarate, as well as other intermediates, are carboxylic acids, which can occur in various ionized forms, including fully protonated, partially protonated, and fully deprotonated forms. Accordingly, the suffix “-ate,” or the acid form, can be used interchangeably to describe both the free acid form as well as any deprotonated form, in particular since the ionized form is known to depend on the pH in which the compound is found. It is understood that carboxylate products or intermediates includes ester forms of carboxylate products or pathway intermediates, such as O-carboxylate and S-carboxylate esters. O- and S-carboxylates can include lower alkyl, that is C1 to C6, branched or straight chain carboxylates. Some such O- or S-carboxylates include, without limitation, methyl, ethyl, n-propyl, n-butyl, i-propyl, sec-butyl, and tert-butyl, pentyl, hexyl O- or S-carboxylates, any of which can further possess an unsaturation, providing for example, propenyl, butenyl, pentyl, and hexenyl O- or S-carboxylates. O-carboxylates can be the product of a biosynthetic pathway. Exemplary O-carboxylates accessed via biosynthetic pathways can include, without limitation, methyl-3-methyl-2-ketoglutarate, methyl-4-hydroxy-4-methyl-2-ketoglutarate, methyl-4-methyl-2-ketoglutaconate, methyl-4-methylene-2-ketoglutarate, methyl-4-methyl-2-ketoglutarate, methyl-4-methyl-2-oxopentanoate, methyl-3-methylglutaconate, methyl-3-methyl-2-hydroxyglutarate, methyl-2-aminoadipate semialdehyde, methyl-2-aminoadipate, methyl-2-oxoadipate, methyl-4-methyl-2-aminoglutarate, ethyl-3-methyl-2-ketoglutarate, ethyl-4-hydroxy-4-methyl-2-ketoglutarate, ethyl-4-methyl-2-ketoglutaconate, ethyl-4-methylene-2-ketoglutarate, ethyl-4-methyl-2-ketoglutarate, ethyl-4-methyl-2-oxopentanoate, ethyl-3-methylglutaconate, ethyl-3-methyl-2-hydroxyglutarate, ethyl-2-aminoadipate semialdehyde, ethyl-2-aminoadipate, ethyl-2-oxoadipate, and ethyl-4-methyl-2-aminoglutarate, n-propyl-3-methyl-2-ketoglutarate, n-propyl-4-hydroxy-4-methyl-2-ketoglutarate, n-propyl-4-methyl-2-ketoglutaconate, n-propyl-4-methylene-2-ketoglutarate, n-propyl-4-methyl-2-ketoglutarate, n-propyl-4-methyl-2-oxopentanoate, n-propyl-3-methylglutaconate, n-propyl-3-methyl-2-hydroxyglutarate, n-propyl-2-aminoadipate semialdehyde, n-propyl-2-aminoadipate, n-propyl-2-oxoadipate, and n-propyl-4-methyl-2-aminoglutarate. Other biosynthetically accessible O-carboxylates can include medium to long chain groups, that is C7-C22, O-carboxylate esters derived from fatty alcohols, such heptyl, octyl, nonyl, decyl, undecyl, lauryl, tridecyl, myristyl, pentadecyl, cetyl, palmitolyl, heptadecyl, stearyl, nonadecyl, arachidyl, heneicosyl, and behenyl alcohols, any one of which can be optionally branched and/or contain unsaturations. O-carboxylate esters can also be accessed via a biochemical or chemical process, such as esterification of a free carboxylic acid product or transesterification of an O- or S-carboxylate. S-carboxylates are exemplified by CoA S-esters, cysteinyl S-esters, alkylthioesters, and various aryl and heteroaryl thioesters.

The non-naturally occurring microbial organisms of the invention can be produced by introducing expressible nucleic acids encoding one or more of the enzymes or proteins participating in one or more propylene biosynthetic pathways. Depending on the host microbial organism chosen for biosynthesis, nucleic acids for some or all of a particular propylene biosynthetic pathway can be expressed. For example, if a chosen host is deficient in one or more enzymes or proteins for a desired biosynthetic pathway, then expressible nucleic acids for the deficient enzyme(s) or protein(s) are introduced into the host for subsequent exogenous expression. Alternatively, if the chosen host exhibits endogenous expression of some pathway genes, but is deficient in others, then an encoding nucleic acid is needed for the deficient enzyme(s) or protein(s) to achieve propylene biosynthesis. Thus, a non-naturally occurring microbial organism of the invention can be produced by introducing exogenous enzyme or protein activities to obtain a desired biosynthetic pathway or a desired biosynthetic pathway can be obtained by introducing one or more exogenous enzyme or protein activities that, together with one or more endogenous enzymes or proteins, produces a desired product such as propylene.

Host microbial organisms can be selected from, and the non-naturally occurring microbial organisms generated in, for example, bacteria, yeast, fungus or any of a variety of other microorganisms applicable to fermentation processes. Exemplary bacteria include species selected from Escherichia coli, Klebsiella oxytoca, Anaerobiospirillum succiniciproducens, Actinobacillus succinogenes, Mannheimia succiniciproducens, Rhizobium etli, Bacillus subtilis, Corynebacterium glutamicum, Gluconobacter oxydans, Zymomonas mobilis, Lactococcus lactis, Lactobacillus plantarum, Streptomyces coelicolor, Clostridium acetobutylicum, Pseudomonas fluorescens, and Pseudomonas putida. Exemplary yeasts or fungi include species selected from Saccharomyces cerevisiae, Schizosaccharomyces pombe, Kluyveromyces lactis, Kluyveromyces marxianus, Aspergillus terreus, Aspergillus niger, Pichia pastoris, Rhizopus arrhizus, Rhizobus oryzae, Yarrowia lipolytica, and the like. E. coli is a particularly useful host organisms since it is a well characterized microbial organism suitable for genetic engineering. Other particularly useful host organisms include yeast such as Saccharomyces cerevisiae. It is understood that any suitable microbial host organism can be used to introduce metabolic and/or genetic modifications to produce a desired product.

Depending on the propylene biosynthetic pathway constituents of a selected host microbial organism, the non-naturally occurring microbial organisms of the invention will include at least one exogenously expressed propylene pathway-encoding nucleic acid and up to all encoding nucleic acids for one or more propylene biosynthetic pathways. For example, propylene biosynthesis can be established in a host deficient in a pathway enzyme or protein through exogenous expression of the corresponding encoding nucleic acid. In a host deficient in all enzymes or proteins of a propylene pathway, exogenous expression of all enzyme or proteins in the pathway can be included, although it is understood that all enzymes or proteins of a pathway can be expressed even if the host contains at least one of the pathway enzymes or proteins. For example, exogenous expression of all enzymes or proteins in a pathway for production of propylene can be included, such as a 2-ketoglutarate methyltransferase and a propylene forming enzyme, or alternatively, a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase II, a 4-methylene-2-ketoglutarate reductase and a propylene forming enzyme, or alternatively a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase I, a 4-methyl-2-ketoglutaconate reductase and a propylene forming enzyme.

Given the teachings and guidance provided herein, those skilled in the art will understand that the number of encoding nucleic acids to introduce in an expressible form will, at least, parallel the propylene pathway deficiencies of the selected host microbial organism. Therefore, a non-naturally occurring microbial organism of the invention can have one, two, three, or four, up to all nucleic acids encoding the enzymes or proteins constituting a propylene biosynthetic pathway disclosed herein. In some embodiments, the non-naturally occurring microbial organisms also can include other genetic modifications that facilitate or optimize propylene biosynthesis or that confer other useful functions onto the host microbial organism. One such other functionality can include, for example, augmentation of the synthesis of one or more of the propylene pathway precursors such as 2-ketoglutarate or pyruvate.

Generally, a host microbial organism is selected such that it produces the precursor of a propylene pathway, either as a naturally produced molecule or as an engineered product that either provides de novo production of a desired precursor or increased production of a precursor naturally produced by the host microbial organism. For example, pyruvate and 2-ketoglutarate are produced naturally in a host organism such as E. coli. A host organism can be engineered to increase production of a precursor, as disclosed herein. In addition, a microbial organism that has been engineered to produce a desired precursor can be used as a host organism and further engineered to express enzymes or proteins of a propylene pathway.

In some embodiments, a non-naturally occurring microbial organism of the invention is generated from a host that contains the enzymatic capability to synthesize propylene. In this specific embodiment it can be useful to increase the synthesis or accumulation of a propylene pathway product to, for example, drive propylene pathway reactions toward propylene production. Increased synthesis or accumulation can be accomplished by, for example, overexpression of nucleic acids encoding one or more of the above-described propylene pathway enzymes or proteins. Overexpression of the enzyme or enzymes and/or protein or proteins of the propylene pathway can occur, for example, through exogenous expression of the endogenous gene or genes, or through exogenous expression of the heterologous gene or genes. Therefore, naturally occurring organisms can be readily generated to be non-naturally occurring microbial organisms of the invention, for example, producing propylene, through overexpression of one, two, three, or four, that is, up to all nucleic acids encoding propylene biosynthetic pathway enzymes or proteins. In addition, a non-naturally occurring organism can be generated by mutagenesis of an endogenous gene that results in an increase in activity of an enzyme in the propylene biosynthetic pathway.

In particularly useful embodiments, exogenous expression of the encoding nucleic acids is employed. Exogenous expression confers the ability to custom tailor the expression and/or regulatory elements to the host and application to achieve a desired expression level that is controlled by the user. However, endogenous expression also can be utilized in other embodiments such as by removing a negative regulatory effector or induction of the gene's promoter when linked to an inducible promoter or other regulatory element. Thus, an endogenous gene having a naturally occurring inducible promoter can be up-regulated by providing the appropriate inducing agent, or the regulatory region of an endogenous gene can be engineered to incorporate an inducible regulatory element, thereby allowing the regulation of increased expression of an endogenous gene at a desired time. Similarly, an inducible promoter can be included as a regulatory element for an exogenous gene introduced into a non-naturally occurring microbial organism.

It is understood that, in methods of the invention, any of the one or more exogenous nucleic acids can be introduced into a microbial organism to produce a non-naturally occurring microbial organism of the invention. The nucleic acids can be introduced so as to confer, for example, a propylene biosynthetic pathway onto the microbial organism. Alternatively, encoding nucleic acids can be introduced to produce an intermediate microbial organism having the biosynthetic capability to catalyze some of the required reactions to confer propylene biosynthetic capability. For example, a non-naturally occurring microbial organism having a propylene biosynthetic pathway can comprise at least two exogenous nucleic acids encoding desired enzymes or proteins, such as the combination of a 2-ketoglutarate methyltransferase and a propylene forming enzyme, or alternatively a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase II and a 4-methylene-2-ketoglutarate reductase, or alternatively a 4-hydroxy-4-methyl-2-ketoglutarate aldolase and a propylene forming enzyme, and the like. Thus, it is understood that any combination of two or more enzymes or proteins of a biosynthetic pathway can be included in a non-naturally occurring microbial organism of the invention. Similarly, it is understood that any combination of three or more enzymes or proteins of a biosynthetic pathway can be included in a non-naturally occurring microbial organism of the invention, for example, a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase II and a 4-methylene-2-ketoglutarate reductase, or alternatively a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase II, a 4-methylene-2-ketoglutarate reductase and a propylene forming enzyme, or alternatively a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase I and a 4-methyl-2-ketoglutaconate reductase, or alternatively a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase I, a 4-methyl-2-ketoglutaconate reductase and a propylene forming enzyme and so forth, as desired, so long as the combination of enzymes and/or proteins of the desired biosynthetic pathway results in production of the corresponding desired product. Similarly, any combination of four, a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase II, a 4-methylene-2-ketoglutarate reductase and a propylene forming enzyme or alternatively a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase I, a 4-methyl-2-ketoglutaconate reductase and a propylene forming enzyme, or more enzymes or proteins of a biosynthetic pathway as disclosed herein can be included in a non-naturally occurring microbial organism of the invention, as desired, so long as the combination of enzymes and/or proteins of the desired biosynthetic pathway results in production of the corresponding desired product.

In addition to the biosynthesis of propylene as described herein, the non-naturally occurring microbial organisms and methods of the invention also can be utilized in various combinations with each other and with other microbial organisms and methods well known in the art to achieve product biosynthesis by other routes. For example, one alternative to produce propylene other than use of the propylene producers is through addition of another microbial organism capable of converting a propylene pathway intermediate to propylene. One such procedure includes, for example, the fermentation of a microbial organism that produces a propylene pathway intermediate. The propylene pathway intermediate can then be used as a substrate for a second microbial organism that converts the propylene pathway intermediate to propylene. The propylene pathway intermediate can be added directly to another culture of the second organism or the original culture of the propylene pathway intermediate producers can be depleted of these microbial organisms by, for example, cell separation, and then subsequent addition of the second organism to the fermentation broth can be utilized to produce the final product without intermediate purification steps.

In other embodiments, the non-naturally occurring microbial organisms and methods of the invention can be assembled in a wide variety of subpathways to achieve biosynthesis of, for example, propylene. In these embodiments, biosynthetic pathways for a desired product of the invention can be segregated into different microbial organisms, and the different microbial organisms can be co-cultured to produce the final product. In such a biosynthetic scheme, the product of one microbial organism is the substrate for a second microbial organism until the final product is synthesized. For example, the biosynthesis of propylene can be accomplished by constructing a microbial organism that contains biosynthetic pathways for conversion of one pathway intermediate to another pathway intermediate or the product. Alternatively, propylene also can be biosynthetically produced from microbial organisms through co-culture or co-fermentation using two organisms in the same vessel, where the first microbial organism produces a propylene intermediate and the second microbial organism converts the intermediate to propylene.

Given the teachings and guidance provided herein, those skilled in the art will understand that a wide variety of combinations and permutations exist for the non-naturally occurring microbial organisms and methods of the invention together with other microbial organisms, with the co-culture of other non-naturally occurring microbial organisms having subpathways and with combinations of other chemical and/or biochemical procedures well known in the art to produce propylene.

Sources of encoding nucleic acids for a propylene pathway enzyme or protein can include, for example, any species where the encoded gene product is capable of catalyzing the referenced reaction. Such species include both prokaryotic and eukaryotic organisms including, but not limited to, bacteria, including archaea and eubacteria, and eukaryotes, including yeast, plant, insect, animal, and mammal, including human. Exemplary species for such sources include, for example, Anaerotruncus colihominis DSM 17241, Bacteroides capillosus ATCC 29799, Campylobacter jejuni, Clostridium botulinum A3 str, Clostridium kluyveri, Clostridium tyrobutyricum, Comamonas testosteroni, Corynebacterium glutamicum, Cupriavidus necator, Escherichia coli, Escherichia coli C, Escherichia coli W, Eubacterium barkeri, Klebsiella pneumoniae, Methanocaldococcus jannaschii, Moorella thermoacetica, Pelotomaculum thermopropionicum, Pseudomonas ochraceae NGJ1, Pseudomonas putida F1, Pseudomonas reinekei MT1, Pseudomonas sp. strain B13, Pseudomonas syringae pv. Glycinea, Pseudomonas syringae pv. phaseolicola PK2, Pseudomonas syringae pv. Pisi, Ralstonia eutropha JMP134, Ralstonia solanacearum, Rattus norvegicus, Rhodococcus opacus, Saccharomyces cerevisiae, Salmonella enterica, Sphingomonas sp. SYK6, Streptomyces coelicolor A3(2), Streptomyces fradiae, Streptomyces roseosporus NRRL 11379, Thermus thermophilus, as well as other exemplary species disclosed herein or available as source organisms for corresponding genes. However, with the complete genome sequence available for now more than 550 species (with more than half of these available on public databases such as the NCBI), including 395 microorganism genomes and a variety of yeast, fungi, plant, and mammalian genomes, the identification of genes encoding the requisite propylene biosynthetic activity for one or more genes in related or distant species, including for example, homologues, orthologs, paralogs and nonorthologous gene displacements of known genes, and the interchange of genetic alterations between organisms is routine and well known in the art. Accordingly, the metabolic alterations allowing biosynthesis of propylene described herein with reference to a particular organism such as E. coli can be readily applied to other microorganisms, including prokaryotic and eukaryotic organisms alike. Given the teachings and guidance provided herein, those skilled in the art will know that a metabolic alteration exemplified in one organism can be applied equally to other organisms.

In some instances, such as when an alternative propylene biosynthetic pathway exists in an unrelated species, propylene biosynthesis can be conferred onto the host species by, for example, exogenous expression of a paralog or paralogs from the unrelated species that catalyzes a similar, yet non-identical metabolic reaction to replace the referenced reaction. Because certain differences among metabolic networks exist between different organisms, those skilled in the art will understand that the actual gene usage between different organisms may differ. However, given the teachings and guidance provided herein, those skilled in the art also will understand that the teachings and methods of the invention can be applied to all microbial organisms using the cognate metabolic alterations to those exemplified herein to construct a microbial organism in a species of interest that will synthesize propylene.

Methods for constructing and testing the expression levels of a non-naturally occurring propylene-producing host can be performed, for example, by recombinant and detection methods well known in the art. Such methods can be found described in, for example, Sambrook et al., Molecular Cloning: A Laboratory Manual, Third Ed., Cold Spring Harbor Laboratory, New York (2001); and Ausubel et al., Current Protocols in Molecular Biology, John Wiley and Sons, Baltimore, Md. (1999).

Exogenous nucleic acid sequences involved in a pathway for production of propylene can be introduced stably or transiently into a host cell using techniques well known in the art including, but not limited to, conjugation, electroporation, chemical transformation, transduction, transfection, and ultrasound transformation. For exogenous expression in E. coli or other prokaryotic cells, some nucleic acid sequences in the genes or cDNAs of eukaryotic nucleic acids can encode targeting signals such as an N-terminal mitochondrial or other targeting signal, which can be removed before transformation into prokaryotic host cells, if desired. For example, removal of a mitochondrial leader sequence led to increased expression in E. coli (Hoffmeister et al., J. Biol. Chem. 280:4329-4338 (2005)). For exogenous expression in yeast or other eukaryotic cells, genes can be expressed in the cytosol without the addition of leader sequence, or can be targeted to mitochondrion or other organelles, or targeted for secretion, by the addition of a suitable targeting sequence such as a mitochondrial targeting or secretion signal suitable for the host cells. Thus, it is understood that appropriate modifications to a nucleic acid sequence to remove or include a targeting sequence can be incorporated into an exogenous nucleic acid sequence to impart desirable properties. Furthermore, genes can be subjected to codon optimization with techniques well known in the art to achieve optimized expression of the proteins.

An expression vector or vectors can be constructed to include one or more propylene biosynthetic pathway encoding nucleic acids as exemplified herein operably linked to expression control sequences functional in the host organism. Expression vectors applicable for use in the microbial host organisms of the invention include, for example, plasmids, phage vectors, viral vectors, episomes and artificial chromosomes, including vectors and selection sequences or markers operable for stable integration into a host chromosome. Additionally, the expression vectors can include one or more selectable marker genes and appropriate expression control sequences. Selectable marker genes also can be included that, for example, provide resistance to antibiotics or toxins, complement auxotrophic deficiencies, or supply critical nutrients not in the culture media. Expression control sequences can include constitutive and inducible promoters, transcription enhancers, transcription terminators, and the like which are well known in the art. When two or more exogenous encoding nucleic acids are to be co-expressed, both nucleic acids can be inserted, for example, into a single expression vector or in separate expression vectors. For single vector expression, the encoding nucleic acids can be operationally linked to one common expression control sequence or linked to different expression control sequences, such as one inducible promoter and one constitutive promoter. The transformation of exogenous nucleic acid sequences involved in a metabolic or synthetic pathway can be confirmed using methods well known in the art. Such methods include, for example, nucleic acid analysis such as Northern blots or polymerase chain reaction (PCR) amplification of mRNA, or immunoblotting for expression of gene products, or other suitable analytical methods to test the expression of an introduced nucleic acid sequence or its corresponding gene product. It is understood by those skilled in the art that the exogenous nucleic acid is expressed in a sufficient amount to produce the desired product, and it is further understood that expression levels can be optimized to obtain sufficient expression using methods well known in the art and as disclosed herein.

In some embodiments, the invention provides a method for producing propylene that includes culturing a non-naturally occurring microbial organism, including a microbial organism having a propylene pathway, the propylene pathway including at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce propylene, the propylene pathway including a 2-ketoglutarate methyltransferase or a propylene forming enzyme (see FIG. 2, steps 1-2). In one aspect, the method includes a microbial organism having a propylene pathway including a 2-ketoglutarate methyltransferase and a propylene forming enzyme (FIG. 2, steps 1 and 2).

In some embodiments, the invention provides a method for producing propylene that includes culturing a non-naturally occurring microbial organism, including a microbial organism having a propylene pathway, the propylene pathway including at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce propylene, the propylene pathway including a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase II, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase I, a 4-methylene-2-ketoglutarate reductase, a 4-methyl-2-ketoglutaconate reductase or a propylene forming enzyme (see FIG. 3, steps A-F). In one aspect, the method includes a microbial organism having a propylene pathway including a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase II, a 4-methylene-2-ketoglutarate reductase and a propylene forming enzyme (see FIG. 3, steps A, B, C and F). In one aspect, the method includes a microbial organism having a propylene pathway including a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase I, a 4-methyl-2-ketoglutaconate reductase and a propylene forming enzyme (FIG. 3, steps A, D, E and F).

In some embodiments, the invention provides a method for producing propylene that includes culturing a non-naturally occurring microbial organism, including a microbial organism having a propylene pathway, the propylene pathway including at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce propylene, the propylene pathway including a leucine aminotransferase, dehydrogenase (deaminating) or oxidase; a 4-methyl-2-oxopentanoate dehydrogenase; an isovaleryl-CoA dehydrogenase; a 3-methylcrotonyl-CoA carboxylase; a 3-methylglutaconyl-CoA hydrolase, transferase or synthetase; a 3-methylglutaconate hydratase; a 3-methyl-2-hydroxyglutarate dehydrogenase; a 3-hydroxy-3-methylglutaryl-CoA dehydratase; or a 3-hydroxy-3-methylglutaryl-CoA lyase (see FIG. 4, steps A-I). In one aspect, the method includes a microbial organism having a propylene pathway including a leucine aminotransferase, dehydrogenase (deaminating) or oxidase; a 4-methyl-2-oxopentanoate dehydrogenase; a isovaleryl-CoA dehydrogenase; a 3-methylcrotonyl-CoA carboxylase; a 3-methylglutaconyl-CoA hydrolase, transferase or synthetase; a 3-methylglutaconate hydratase; a 3-methyl-2-hydroxyglutarate dehydrogenase and a propylene forming enzyme (see FIG. 4, steps A-G and FIG. 2, step 2). In one aspect, the method includes a microbial organism having a propylene pathway including a 3-methylglutaconyl-CoA hydrolase, transferase or synthetase; a 3-methylglutaconate hydratase; a 3-methyl-2-hydroxyglutarate dehydrogenase; a 3-hydroxy-3-methylglutaryl-CoA dehydratase; a 3-hydroxy-3-methylglutaryl-CoA lyase and a propylene forming enzyme (see FIG. 4, steps I, H, E-G and FIG. 2, step 2). Sources of encoding nucleic acids for a propylene pathway enzyme or protein described above are well known in the art and can be obtained from a variety of species including, but limited to, those exemplified herein.

In some embodiments, the invention provides a method for producing propylene that includes culturing a non-naturally occurring microbial organism, including a microbial organism having a propylene pathway, the propylene pathway including at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce propylene, the propylene pathway including a lysine 6-aminotransferase, a 6-dehydrogenase (deaminating) or 6-oxidase; an 2-aminoadipate dehydrogenase; an 2-aminoadipate mutase; a 4-methyl-2-aminoglutarate aminotransferase, dehydrogenase (deaminating) or oxidase; a 2-aminoadipate aminotransferase, dehydrogenase (deaminating) or oxidase; or a 2-oxoadipate mutase (see FIG. 5, steps A-F). In one aspect, the method includes a microbial organism having a propylene pathway including a lysine 6-aminotransferase, 6-dehydrogenase (deaminating) or 6-oxidase; an 2-aminoadipate dehydrogenase, an 2-aminoadipate mutase; a 4-methyl-2-aminoglutarate aminotransferase, dehydrogenase (deaminating) or oxidase; and a propylene forming enzyme (see FIG. 5, steps A-D, FIG. 3, step F). In one aspect, the method includes a microbial organism having a propylene pathway including a lysine 6-aminotransferase, 6-dehydrogenase (deaminating) or 6-oxidase; a 2-aminoadipate dehydrogenase; an 2-aminoadipate aminotransferase, dehydrogenase (deaminating) or oxidase; an 2-oxoadipate mutase; and a propylene forming enzyme (see FIG. 5, steps A, B, E and F, FIG. 3, step F). Sources of encoding nucleic acids for a propylene pathway enzyme or protein described above are well known in the art and can be obtained from a variety of species including, but limited to, those exemplified herein.

Suitable purification and/or assays to test for the production of propylene can be performed using well known methods. Suitable replicates such as triplicate cultures can be grown for each engineered strain to be tested. For example, product and byproduct formation in the engineered production host can be monitored. The final product and intermediates, and other organic compounds, can be analyzed by methods such as HPLC (High Performance Liquid Chromatography), GC-MS (Gas Chromatography-Mass Spectroscopy) and LC-MS (Liquid Chromatography-Mass Spectroscopy) or other suitable analytical methods using routine procedures well known in the art. The release of product in the fermentation broth can also be tested with the culture supernatant. Byproducts and residual glucose can be quantified by HPLC using, for example, a refractive index detector for glucose and alcohols, and a UV detector for organic acids (Lin et al., Biotechnol. Bioeng. 90:775-779 (2005)), or other suitable assay and detection methods well known in the art. The individual enzyme or protein activities from the exogenous DNA sequences can also be assayed using methods well known in the art. For typical Assay Methods, see Manual on Hydrocarbon Analysis (ASTM Manula Series, A. W. Drews, ed., 6^(th) edition, 1998, American Society for Testing and Materials, Baltimore, Md.

The propylene can be separated from other components in the culture using a variety of methods well known in the art. Such separation methods include, for example, extraction procedures as well as methods that include continuous liquid-liquid extraction, pervaporation, membrane filtration, membrane separation, reverse osmosis, electrodialysis, distillation, crystallization, centrifugation, extractive filtration, ion exchange chromatography, size exclusion chromatography, adsorption chromatography, and ultrafiltration. All of the above methods are well known in the art.

Any of the non-naturally occurring microbial organisms described herein can be cultured to produce and/or secrete the biosynthetic products of the invention. For example, the propylene producers can be cultured for the biosynthetic production of propylene.

For the production of propylene, the recombinant strains are cultured in a medium with carbon source and other essential nutrients. It is sometimes desirable and can be highly desirable to maintain anaerobic conditions in the fermenter to reduce the cost of the overall process. Such conditions can be obtained, for example, by first sparging the medium with nitrogen and then sealing the flasks with a septum and crimp-cap. For strains where growth is not observed anaerobically, microaerobic or substantially anaerobic conditions can be applied by perforating the septum with a small hole for limited aeration. Exemplary anaerobic conditions have been described previously and are well-known in the art. Exemplary aerobic and anaerobic conditions are described, for example, in United State publication 2009/0047719, filed Aug. 10, 2007. Fermentations can be performed in a batch, fed-batch or continuous manner, as disclosed herein.

If desired, the pH of the medium can be maintained at a desired pH, in particular neutral pH, such as a pH of around 7 by addition of a base, such as NaOH or other bases, or acid, as needed to maintain the culture medium at a desirable pH. The growth rate can be determined by measuring optical density using a spectrophotometer (600 nm), and the glucose uptake rate by monitoring carbon source depletion over time.

The growth medium can include, for example, any carbohydrate source which can supply a source of carbon to the non-naturally occurring microorganism. Such sources include, for example, sugars such as glucose, xylose, arabinose, galactose, mannose, fructose, sucrose and starch. Other sources of carbohydrate include, for example, renewable feedstocks and biomass. Exemplary types of biomasses that can be used as feedstocks in the methods of the invention include cellulosic biomass, hemicellulosic biomass and lignin feedstocks or portions of feedstocks. Such biomass feedstocks contain, for example, carbohydrate substrates useful as carbon sources such as glucose, xylose, arabinose, galactose, mannose, fructose and starch. Given the teachings and guidance provided herein, those skilled in the art will understand that renewable feedstocks and biomass other than those exemplified above also can be used for culturing the microbial organisms of the invention for the production of propylene.

In addition to renewable feedstocks such as those exemplified above, the propylene microbial organisms of the invention also can be modified for growth on syngas as its source of carbon. In this specific embodiment, one or more proteins or enzymes are expressed in the propylene producing organisms to provide a metabolic pathway for utilization of syngas or other gaseous carbon source.

Synthesis gas, also known as syngas or producer gas, is the major product of gasification of coal and of carbonaceous materials such as biomass materials, including agricultural crops and residues. Syngas is a mixture primarily of H₂ and CO and can be obtained from the gasification of any organic feedstock, including but not limited to coal, coal oil, natural gas, biomass, and waste organic matter. Gasification is generally carried out under a high fuel to oxygen ratio. Although largely H₂ and CO, syngas can also include CO₂ and other gases in smaller quantities. Thus, synthesis gas provides a cost effective source of gaseous carbon such as CO and, additionally, CO₂.

The Wood-Ljungdahl pathway catalyzes the conversion of CO and H₂ to acetyl-CoA and other products such as acetate. Organisms capable of utilizing CO and syngas also generally have the capability of utilizing CO₂ and CO₂/H₂ mixtures through the same basic set of enzymes and transformations encompassed by the Wood-Ljungdahl pathway. H₂-dependent conversion of CO₂ to acetate by microorganisms was recognized long before it was revealed that CO also could be used by the same organisms and that the same pathways were involved. Many acetogens have been shown to grow in the presence of CO₂ and produce compounds such as acetate as long as hydrogen is present to supply the necessary reducing equivalents (see for example, Drake, Acetogenesis, pp. 3-60 Chapman and Hall, New York, (1994)). This can be summarized by the following equation:

2CO₂+4H₂ +n ADP+n Pi→CH₃COOH+2H₂O+n ATP

Hence, non-naturally occurring microorganisms possessing the Wood-Ljungdahl pathway can utilize CO₂ and H₂ mixtures as well for the production of acetyl-CoA and other desired products.

The Wood-Ljungdahl pathway is well known in the art and consists of 12 reactions which can be separated into two branches: (1) methyl branch and (2) carbonyl branch. The methyl branch converts syngas to methyl-tetrahydrofolate (methyl-THF) whereas the carbonyl branch converts methyl-THF to acetyl-CoA. The reactions in the methyl branch are catalyzed in order by the following enzymes or proteins: ferredoxin oxidoreductase, formate dehydrogenase, formyltetrahydrofolate synthetase, methenyltetrahydrofolate cyclodehydratase, methylenetetrahydrofolate dehydrogenase and methylenetetrahydrofolate reductase. The reactions in the carbonyl branch are catalyzed in order by the following enzymes or proteins: methyltetrahydrofolate:corrinoid protein methyltransferase (for example, AcsE), corrinoid iron-sulfur protein, nickel-protein assembly protein (for example, AcsF), ferredoxin, acetyl-CoA synthase, carbon monoxide dehydrogenase and nickel-protein assembly protein (for example, CooC). Following the teachings and guidance provided herein for introducing a sufficient number of encoding nucleic acids to generate a propylene pathway, those skilled in the art will understand that the same engineering design also can be performed with respect to introducing at least the nucleic acids encoding the Wood-Ljungdahl enzymes or proteins absent in the host organism. Therefore, introduction of one or more encoding nucleic acids into the microbial organisms of the invention such that the modified organism contains the complete Wood-Ljungdahl pathway will confer syngas utilization ability.

Additionally, the reductive (reverse) tricarboxylic acid cycle coupled with carbon monoxide dehydrogenase and/or hydrogenase activities can also be used for the conversion of CO, CO₂ and/or H₂ to acetyl-CoA and other products such as acetate. Organisms capable of fixing carbon via the reductive TCA pathway can utilize one or more of the following enzymes: ATP citrate-lyase, citrate lyase, aconitase, isocitrate dehydrogenase, alpha-ketoglutarate:ferredoxin oxidoreductase, succinyl-CoA synthetase, succinyl-CoA transferase, fumarate reductase, fumarase, malate dehydrogenase, NAD(P)H:ferredoxin oxidoreductase, carbon monoxide dehydrogenase, and hydrogenase. Specifically, the reducing equivalents extracted from CO and/or H₂ by carbon monoxide dehydrogenase and hydrogenase are utilized to fix CO₂ via the reductive TCA cycle into acetyl-CoA or acetate. Acetate can be converted to acetyl-CoA by enzymes such as acetyl-CoA transferase, acetate kinase/phosphotransacetylase, and acetyl-CoA synthetase. Acetyl-CoA can be converted to the p-toluate, terepathalate, or (2-hydroxy-3-methyl-4-oxobutoxy)phosphonate precursors, glyceraldehyde-3-phosphate, phosphoenolpyruvate, and pyruvate, by pyruvate:ferredoxin oxidoreductase and the enzymes of gluconeogenesis. Following the teachings and guidance provided herein for introducing a sufficient number of encoding nucleic acids to generate a p-toluate, terephthalate or (2-hydroxy-3-methyl-4-oxobutoxy)phosphonate pathway, those skilled in the art will understand that the same engineering design also can be performed with respect to introducing at least the nucleic acids encoding the reductive TCA pathway enzymes or proteins absent in the host organism. Therefore, introduction of one or more encoding nucleic acids into the microbial organisms of the invention such that the modified organism contains the complete reductive TCA pathway will confer syngas utilization ability.

Accordingly, given the teachings and guidance provided herein, those skilled in the art will understand that a non-naturally occurring microbial organism can be produced that secretes the biosynthesized compounds of the invention when grown on a carbon source such as a carbohydrate. Such compounds include, for example, propylene and any of the intermediate metabolites in the propylene pathway. All that is required is to engineer in one or more of the required enzyme or protein activities to achieve biosynthesis of the desired compound or intermediate including, for example, inclusion of some or all of the propylene biosynthetic pathways. Accordingly, the invention provides a non-naturally occurring microbial organism that produces and/or secretes propylene when grown on a carbohydrate or other carbon source and produces and/or secretes any of the intermediate metabolites shown in the propylene pathway when grown on a carbohydrate or other carbon source. The propylene producing microbial organisms of the invention can initiate synthesis from an intermediate, for example, 3-methyle-ketoglutarate, 4-hydroxy-4-methyl-2-ketoglutarate, 4-methylene-2-ketoglutarate, 4-methyl-2-ketoglutaconate, or 4-methyl-2-ketoglutarate.

The non-naturally occurring microbial organisms of the invention are constructed using methods well known in the art as exemplified herein to exogenously express at least one nucleic acid encoding a propylene pathway enzyme or protein in sufficient amounts to produce propylene. It is understood that the microbial organisms of the invention are cultured under conditions sufficient to produce propylene. Following the teachings and guidance provided herein, the non-naturally occurring microbial organisms of the invention can achieve biosynthesis of propylene resulting in intracellular concentrations between about 0.001-2000 mM or more. Generally, the intracellular concentration of propylene is between about 3-1500 mM, particularly between about 5-1250 mM and more particularly between about 8-1000 mM, including about 100 mM, 200 mM, 500 mM, 800 mM, or more. Intracellular concentrations between and above each of these exemplary ranges also can be achieved from the non-naturally occurring microbial organisms of the invention.

In some embodiments, culture conditions include anaerobic or substantially anaerobic growth or maintenance conditions. Exemplary anaerobic conditions have been described previously and are well known in the art. Exemplary anaerobic conditions for fermentation processes are described herein and are described, for example, in U.S. publication 2009/0047719, filed Aug. 10, 2007. Any of these conditions can be employed with the non-naturally occurring microbial organisms as well as other anaerobic conditions well known in the art. Under such anaerobic or substantially anaerobic conditions, the propylene producers can synthesize propylene at intracellular concentrations of 5-10 mM or more as well as all other concentrations exemplified herein. It is understood that, even though the above description refers to intracellular concentrations, propylene producing microbial organisms can produce propylene intracellularly and/or secrete the product into the culture medium.

In addition to the culturing and fermentation conditions disclosed herein, growth condition for achieving biosynthesis of propylene can include the addition of an osmoprotectant to the culturing conditions. In certain embodiments, the non-naturally occurring microbial organisms of the invention can be sustained, cultured or fermented as described herein in the presence of an osmoprotectant. Briefly, an osmoprotectant refers to a compound that acts as an osmolyte and helps a microbial organism as described herein survive osmotic stress. Osmoprotectants include, but are not limited to, betaines, amino acids, and the sugar trehalose. Non-limiting examples of such are glycine betaine, praline betaine, dimethylthetin, dimethylslfonioproprionate, 3-dimethylsulfonio-2-methylproprionate, pipecolic acid, dimethylsulfonioacetate, choline, L-carnitine and ectoine. In one aspect, the osmoprotectant is glycine betaine. It is understood to one of ordinary skill in the art that the amount and type of osmoprotectant suitable for protecting a microbial organism described herein from osmotic stress will depend on the microbial organism used. The amount of osmoprotectant in the culturing conditions can be, for example, no more than about 0.1 mM, no more than about 0.5 mM, no more than about 1.0 mM, no more than about 1.5 mM, no more than about 2.0 mM, no more than about 2.5 mM, no more than about 3.0 mM, no more than about 5.0 mM, no more than about 7.0 mM, no more than about 10 mM, no more than about 50 mM, no more than about 100 mM or no more than about 500 mM.

The culture conditions can include, for example, liquid culture procedures as well as fermentation and other large scale culture procedures. As described herein, particularly useful yields of the biosynthetic products of the invention can be obtained under anaerobic or substantially anaerobic culture conditions.

As described herein, one exemplary growth condition for achieving biosynthesis of propylene includes anaerobic culture or fermentation conditions. In certain embodiments, the non-naturally occurring microbial organisms of the invention can be sustained, cultured or fermented under anaerobic or substantially anaerobic conditions. Briefly, anaerobic conditions refers to an environment devoid of oxygen. Substantially anaerobic conditions include, for example, a culture, batch fermentation or continuous fermentation such that the dissolved oxygen concentration in the medium remains between 0 and 10% of saturation. Substantially anaerobic conditions also includes growing or resting cells in liquid medium or on solid agar inside a sealed chamber maintained with an atmosphere of less than 1% oxygen. The percent of oxygen can be maintained by, for example, sparging the culture with an N₂/CO₂ mixture or other suitable non-oxygen gas or gases.

The culture conditions described herein can be scaled up and grown continuously for manufacturing of propylene. Exemplary growth procedures include, for example, fed-batch fermentation and batch separation; fed-batch fermentation and continuous separation, or continuous fermentation and continuous separation. All of these processes are well known in the art. Fermentation procedures are particularly useful for the biosynthetic production of commercial quantities of propylene. Generally, and as with non-continuous culture procedures, the continuous and/or near-continuous production of propylene will include culturing a non-naturally occurring propylene producing organism of the invention in sufficient nutrients and medium to sustain and/or nearly sustain growth in an exponential phase. Continuous culture under such conditions can include, for example, growth for 1 day, 2, 3, 4, 5, 6 or 7 days or more. Additionally, continuous culture can include longer time periods of 1 week, 2, 3, 4 or 5 or more weeks and up to several months. Alternatively, organisms of the invention can be cultured for hours, if suitable for a particular application. It is to be understood that the continuous and/or near-continuous culture conditions also can include all time intervals in between these exemplary periods. It is further understood that the time of culturing the microbial organism of the invention is for a sufficient period of time to produce a sufficient amount of product for a desired purpose.

Fermentation procedures are well known in the art. Briefly, fermentation for the biosynthetic production of propylene can be utilized in, for example, fed-batch fermentation and batch separation; fed-batch fermentation and continuous separation, or continuous fermentation and continuous separation. Examples of batch and continuous fermentation procedures are well known in the art.

In addition to the above fermentation procedures using the propylene producers of the invention for continuous production of substantial quantities of propylene, the propylene producers also can be, for example, simultaneously subjected to chemical synthesis procedures to convert the product to other compounds or the product can be separated from the fermentation culture and sequentially subjected to chemical or enzymatic conversion to convert the product to other compounds, if desired.

To generate better producers, metabolic modeling can be utilized to optimize growth conditions. Modeling can also be used to design gene knockouts that additionally optimize utilization of the pathway (see, for example, U.S. patent publications US 2002/0012939, US 2003/0224363, US 2004/0029149, US 2004/0072723, US 2003/0059792, US 2002/0168654 and US 2004/0009466, and U.S. Pat. No. 7,127,379). Modeling analysis allows reliable predictions of the effects on cell growth of shifting the metabolism towards more efficient production of propylene.

One computational method for identifying and designing metabolic alterations favoring biosynthesis of a desired product is the OptKnock computational framework (Burgard et al., Biotechnol. Bioeng. 84:647-657 (2003)). OptKnock is a metabolic modeling and simulation program that suggests gene deletion or disruption strategies that result in genetically stable microorganisms which overproduce the target product. Specifically, the framework examines the complete metabolic and/or biochemical network of a microorganism in order to suggest genetic manipulations that force the desired biochemical to become an obligatory byproduct of cell growth. By coupling biochemical production with cell growth through strategically placed gene deletions or other functional gene disruption, the growth selection pressures imposed on the engineered strains after long periods of time in a bioreactor lead to improvements in performance as a result of the compulsory growth-coupled biochemical production. Lastly, when gene deletions are constructed there is a negligible possibility of the designed strains reverting to their wild-type states because the genes selected by OptKnock are to be completely removed from the genome. Therefore, this computational methodology can be used to either identify alternative pathways that lead to biosynthesis of a desired product or used in connection with the non-naturally occurring microbial organisms for further optimization of biosynthesis of a desired product.

Briefly, OptKnock is a term used herein to refer to a computational method and system for modeling cellular metabolism. The OptKnock program relates to a framework of models and methods that incorporate particular constraints into flux balance analysis (FBA) models. These constraints include, for example, qualitative kinetic information, qualitative regulatory information, and/or DNA microarray experimental data. OptKnock also computes solutions to various metabolic problems by, for example, tightening the flux boundaries derived through flux balance models and subsequently probing the performance limits of metabolic networks in the presence of gene additions or deletions. OptKnock computational framework allows the construction of model formulations that allow an effective query of the performance limits of metabolic networks and provides methods for solving the resulting mixed-integer linear programming problems. The metabolic modeling and simulation methods referred to herein as OptKnock are described in, for example, U.S. publication 2002/0168654, filed Jan. 10, 2002, in International Patent No. PCT/US02/00660, filed Jan. 10, 2002, and U.S. publication 2009/0047719, filed Aug. 10, 2007.

Another computational method for identifying and designing metabolic alterations favoring biosynthetic production of a product is a metabolic modeling and simulation system termed SimPheny®. This computational method and system is described in, for example, U.S. publication 2003/0233218, filed Jun. 14, 2002, and in International Patent Application No. PCT/US03/18838, filed Jun. 13, 2003. SimPheny® is a computational system that can be used to produce a network model in silico and to simulate the flux of mass, energy or charge through the chemical reactions of a biological system to define a solution space that contains any and all possible functionalities of the chemical reactions in the system, thereby determining a range of allowed activities for the biological system. This approach is referred to as constraints-based modeling because the solution space is defined by constraints such as the known stoichiometry of the included reactions as well as reaction thermodynamic and capacity constraints associated with maximum fluxes through reactions. The space defined by these constraints can be interrogated to determine the phenotypic capabilities and behavior of the biological system or of its biochemical components.

These computational approaches are consistent with biological realities because biological systems are flexible and can reach the same result in many different ways. Biological systems are designed through evolutionary mechanisms that have been restricted by fundamental constraints that all living systems must face. Therefore, constraints-based modeling strategy embraces these general realities. Further, the ability to continuously impose further restrictions on a network model via the tightening of constraints results in a reduction in the size of the solution space, thereby enhancing the precision with which physiological performance or phenotype can be predicted.

Given the teachings and guidance provided herein, those skilled in the art will be able to apply various computational frameworks for metabolic modeling and simulation to design and implement biosynthesis of a desired compound in host microbial organisms. Such metabolic modeling and simulation methods include, for example, the computational systems exemplified above as SimPheny® and OptKnock. For illustration of the invention, some methods are described herein with reference to the OptKnock computation framework for modeling and simulation. Those skilled in the art will know how to apply the identification, design and implementation of the metabolic alterations using OptKnock to any of such other metabolic modeling and simulation computational frameworks and methods well known in the art.

The methods described above will provide one set of metabolic reactions to disrupt. Elimination of each reaction within the set or metabolic modification can result in a desired product as an obligatory product during the growth phase of the organism. Because the reactions are known, a solution to the bilevel OptKnock problem also will provide the associated gene or genes encoding one or more enzymes that catalyze each reaction within the set of reactions. Identification of a set of reactions and their corresponding genes encoding the enzymes participating in each reaction is generally an automated process, accomplished through correlation of the reactions with a reaction database having a relationship between enzymes and encoding genes.

Once identified, the set of reactions that are to be disrupted in order to achieve production of a desired product are implemented in the target cell or organism by functional disruption of at least one gene encoding each metabolic reaction within the set. One particularly useful means to achieve functional disruption of the reaction set is by deletion of each encoding gene. However, in some instances, it can be beneficial to disrupt the reaction by other genetic aberrations including, for example, mutation, deletion of regulatory regions such as promoters or cis binding sites for regulatory factors, or by truncation of the coding sequence at any of a number of locations. These latter aberrations, resulting in less than total deletion of the gene set can be useful, for example, when rapid assessments of the coupling of a product are desired or when genetic reversion is less likely to occur.

To identify additional productive solutions to the above described bilevel OptKnock problem which lead to further sets of reactions to disrupt or metabolic modifications that can result in the biosynthesis, including growth-coupled biosynthesis of a desired product, an optimization method, termed integer cuts, can be implemented. This method proceeds by iteratively solving the OptKnock problem exemplified above with the incorporation of an additional constraint referred to as an integer cut at each iteration. Integer cut constraints effectively prevent the solution procedure from choosing the exact same set of reactions identified in any previous iteration that obligatorily couples product biosynthesis to growth. For example, if a previously identified growth-coupled metabolic modification specifies reactions 1, 2, and 3 for disruption, then the following constraint prevents the same reactions from being simultaneously considered in subsequent solutions. The integer cut method is well known in the art and can be found described in, for example, Burgard et al., Biotechnol. Prog. 17:791-797 (2001). As with all methods described herein with reference to their use in combination with the OptKnock computational framework for metabolic modeling and simulation, the integer cut method of reducing redundancy in iterative computational analysis also can be applied with other computational frameworks well known in the art including, for example, SimPheny®.

The methods exemplified herein allow the construction of cells and organisms that biosynthetically produce a desired product, including the obligatory coupling of production of a target biochemical product to growth of the cell or organism engineered to harbor the identified genetic alterations. Therefore, the computational methods described herein allow the identification and implementation of metabolic modifications that are identified by an in silico method selected from OptKnock or SimPheny®. The set of metabolic modifications can include, for example, addition of one or more biosynthetic pathway enzymes and/or functional disruption of one or more metabolic reactions including, for example, disruption by gene deletion.

As discussed above, the OptKnock methodology was developed on the premise that mutant microbial networks can be evolved towards their computationally predicted maximum-growth phenotypes when subjected to long periods of growth selection. In other words, the approach leverages an organism's ability to self-optimize under selective pressures. The OptKnock framework allows for the exhaustive enumeration of gene deletion combinations that force a coupling between biochemical production and cell growth based on network stoichiometry. The identification of optimal gene/reaction knockouts requires the solution of a bilevel optimization problem that chooses the set of active reactions such that an optimal growth solution for the resulting network overproduces the biochemical of interest (Burgard et al., Biotechnol. Bioeng. 84:647-657 (2003)).

An in silico stoichiometric model of E. coli metabolism can be employed to identify essential genes for metabolic pathways as exemplified previously and described in, for example, U.S. patent publications US 2002/0012939, US 2003/0224363, US 2004/0029149, US 2004/0072723, US 2003/0059792, US 2002/0168654 and US 2004/0009466, and in U.S. Pat. No. 7,127,379. As disclosed herein, the OptKnock mathematical framework can be applied to pinpoint gene deletions leading to the growth-coupled production of a desired product. Further, the solution of the bilevel OptKnock problem provides only one set of deletions. To enumerate all meaningful solutions, that is, all sets of knockouts leading to growth-coupled production formation, an optimization technique, termed integer cuts, can be implemented. This entails iteratively solving the OptKnock problem with the incorporation of an additional constraint referred to as an integer cut at each iteration, as discussed above.

As disclosed herein, a nucleic acid encoding a desired activity of a propylene pathway can be introduced into a host organism. In some cases, it can be desirable to modify an activity of a propylene pathway enzyme or protein to increase production of propylene. For example, known mutations that increase the activity of a protein or enzyme can be introduced into an encoding nucleic acid molecule. Additionally, optimization methods can be applied to increase the activity of an enzyme or protein and/or decrease an inhibitory activity, for example, decrease the activity of a negative regulator.

One such optimization method is directed evolution. Directed evolution is a powerful approach that involves the introduction of mutations targeted to a specific gene in order to improve and/or alter the properties of an enzyme. Improved and/or altered enzymes can be identified through the development and implementation of sensitive high-throughput screening assays that allow the automated screening of many enzyme variants (for example, >10⁴). Iterative rounds of mutagenesis and screening typically are performed to afford an enzyme with optimized properties. Computational algorithms that can help to identify areas of the gene for mutagenesis also have been developed and can significantly reduce the number of enzyme variants that need to be generated and screened. Numerous directed evolution technologies have been developed (for reviews, see Hibbert et al., Biomol.Eng 22:11-19 (2005); Huisman and Lalonde, In Biocatalysis in the pharmaceutical and biotechnology industries pgs. 717-742 (2007), Patel (ed.), CRC Press; Otten and Quax. Biomol. Eng 22:1-9 (2005).; and Sen et al., Appl Biochem. Biotechnol 143:212-223 (2007)) to be effective at creating diverse variant libraries, and these methods have been successfully applied to the improvement of a wide range of properties across many enzyme classes. Enzyme characteristics that have been improved and/or altered by directed evolution technologies include, for example: selectivity/specificity, for conversion of non-natural substrates; temperature stability, for robust high temperature processing; pH stability, for bioprocessing under lower or higher pH conditions; substrate or product tolerance, so that high product titers can be achieved; binding (K_(m)), including broadening substrate binding to include non-natural substrates; inhibition (K_(i)), to remove inhibition by products, substrates, or key intermediates; activity (kcat), to increases enzymatic reaction rates to achieve desired flux; expression levels, to increase protein yields and overall pathway flux; oxygen stability, for operation of air sensitive enzymes under aerobic conditions; and anaerobic activity, for operation of an aerobic enzyme in the absence of oxygen.

Described below in more detail are exemplary methods that have been developed for the mutagenesis and diversification of genes to target desired properties of specific enzymes. Such methods are well known to those skilled in the art. Any of these can be used to alter and/or optimize the activity of a propylene pathway enzyme or protein.

EpPCR (Pritchard et al., J Theor. Biol. 234:497-509 (2005)) introduces random point mutations by reducing the fidelity of DNA polymerase in PCR reactions by the addition of Mn²⁺ ions, by biasing dNTP concentrations, or by other conditional variations. The five step cloning process to confine the mutagenesis to the target gene of interest involves: 1) error-prone PCR amplification of the gene of interest; 2) restriction enzyme digestion; 3) gel purification of the desired DNA fragment; 4) ligation into a vector; 5) transformation of the gene variants into a suitable host and screening of the library for improved performance. This method can generate multiple mutations in a single gene simultaneously, which can be useful to screen a larger number of potential variants having a desired activity. A high number of mutants can be generated by EpPCR, so a high-throughput screening assay or a selection method, for example, using robotics, is useful to identify those with desirable characteristics.

Error-prone Rolling Circle Amplification (epRCA) (Fujii et al., Nucleic Acids Res. 32:e145 (2004); and Fujii et al., Nat. Protoc. 1:2493-2497 (2006)) has many of the same elements as epPCR except a whole circular plasmid is used as the template and random 6-mers with exonuclease resistant thiophosphate linkages on the last 2 nucleotides are used to amplify the plasmid followed by transformation into cells in which the plasmid is re-circularized at tandem repeats. Adjusting the Mn²⁺ concentration can vary the mutation rate somewhat. This technique uses a simple error-prone, single-step method to create a full copy of the plasmid with 3-4 mutations/kbp. No restriction enzyme digestion or specific primers are required. Additionally, this method is typically available as a commercially available kit.

DNA or Family Shuffling (Stemmer, Proc Natl Acad Sci USA 91:10747-10751 (1994)); and Stemmer, Nature 370:389-391 (1994)) typically involves digestion of two or more variant genes with nucleases such as Dnase I or EndoV to generate a pool of random fragments that are reassembled by cycles of annealing and extension in the presence of DNA polymerase to create a library of chimeric genes. Fragments prime each other and recombination occurs when one copy primes another copy (template switch). This method can be used with >1 kbp DNA sequences. In addition to mutational recombinants created by fragment reassembly, this method introduces point mutations in the extension steps at a rate similar to error-prone PCR. The method can be used to remove deleterious, random and neutral mutations.

Staggered Extension (StEP) (Zhao et al., Nat. Biotechnol. 16:258-261 (1998)) entails template priming followed by repeated cycles of 2 step PCR with denaturation and very short duration of annealing/extension (as short as 5 sec). Growing fragments anneal to different templates and extend further, which is repeated until full-length sequences are made. Template switching means most resulting fragments have multiple parents. Combinations of low-fidelity polymerases (Taq and Mutazyme) reduce error-prone biases because of opposite mutational spectra.

In Random Priming Recombination (RPR) random sequence primers are used to generate many short DNA fragments complementary to different segments of the template (Shao et al., Nucleic Acids Res 26:681-683 (1998)). Base misincorporation and mispriming via epPCR give point mutations. Short DNA fragments prime one another based on homology and are recombined and reassembled into full-length by repeated thermocycling. Removal of templates prior to this step assures low parental recombinants. This method, like most others, can be performed over multiple iterations to evolve distinct properties. This technology avoids sequence bias, is independent of gene length, and requires very little parent DNA for the application.

In Heteroduplex Recombination linearized plasmid DNA is used to form heteroduplexes that are repaired by mismatch repair (Volkov et al, Nucleic Acids Res. 27:e18 (1999); and Volkov et al., Methods Enzymol. 328:456-463 (2000)). The mismatch repair step is at least somewhat mutagenic. Heteroduplexes transform more efficiently than linear homoduplexes. This method is suitable for large genes and whole operons.

Random Chimeragenesis on Transient Templates (RACHITT) (Coco et al., Nat. Biotechnol. 19:354-359 (2001)) employs Dnase I fragmentation and size fractionation of single stranded DNA (ssDNA). Homologous fragments are hybridized in the absence of polymerase to a complementary ssDNA scaffold. Any overlapping unhybridized fragment ends are trimmed down by an exonuclease. Gaps between fragments are filled in and then ligated to give a pool of full-length diverse strands hybridized to the scaffold, which contains U to preclude amplification. The scaffold then is destroyed and is replaced by a new strand complementary to the diverse strand by PCR amplification. The method involves one strand (scaffold) that is from only one parent while the priming fragments derive from other genes; the parent scaffold is selected against. Thus, no reannealing with parental fragments occurs. Overlapping fragments are trimmed with an exonuclease. Otherwise, this is conceptually similar to DNA shuffling and StEP. Therefore, there should be no siblings, few inactives, and no unshuffled parentals. This technique has advantages in that few or no parental genes are created and many more crossovers can result relative to standard DNA shuffling.

Recombined Extension on Truncated templates (RETT) entails template switching of unidirectionally growing strands from primers in the presence of unidirectional ssDNA fragments used as a pool of templates (Lee et al., J. Molec. Catalysis 26:119-129 (2003)). No DNA endonucleases are used. Unidirectional ssDNA is made by DNA polymerase with random primers or serial deletion with exonuclease. Unidirectional ssDNA are only templates and not primers. Random priming and exonucleases do not introduce sequence bias as true of enzymatic cleavage of DNA shuffling/RACHITT. RETT can be easier to optimize than StEP because it uses normal PCR conditions instead of very short extensions. Recombination occurs as a component of the PCR steps, that is, no direct shuffling. This method can also be more random than StEP due to the absence of pauses.

In Degenerate Oligonucleotide Gene Shuffling (DOGS) degenerate primers are used to control recombination between molecules; (Bergquist and Gibbs, Methods Mol. Biol. 352:191-204 (2007); Bergquist et al., Biomol. Eng 22:63-72 (2005); Gibbs et al., Gene 271:13-20 (2001)) this can be used to control the tendency of other methods such as DNA shuffling to regenerate parental genes. This method can be combined with random mutagenesis (epPCR) of selected gene segments. This can be a good method to block the reformation of parental sequences. No endonucleases are needed. By adjusting input concentrations of segments made, one can bias towards a desired backbone. This method allows DNA shuffling from unrelated parents without restriction enzyme digests and allows a choice of random mutagenesis methods.

Incremental Truncation for the Creation of Hybrid Enzymes (ITCHY) creates a combinatorial library with 1 base pair deletions of a gene or gene fragment of interest (Ostermeier et al., Proc. Natl. Acad. Sci. USA 96:3562-3567 (1999); and Ostermeier et al., Nat. Biotechnol. 17:1205-1209 (1999)). Truncations are introduced in opposite direction on pieces of 2 different genes. These are ligated together and the fusions are cloned. This technique does not require homology between the 2 parental genes. When ITCHY is combined with DNA shuffling, the system is called SCRATCHY (see below). A major advantage of both is no need for homology between parental genes; for example, functional fusions between an E. coli and a human gene were created via ITCHY. When ITCHY libraries are made, all possible crossovers are captured.

Thio-Incremental Truncation for the Creation of Hybrid Enzymes (THIO-ITCHY) is similar to ITCHY except that phosphothioate dNTPs are used to generate truncations (Lutz et al., Nucleic Acids Res 29:E16 (2001)). Relative to ITCHY, THIO-ITCHY can be easier to optimize, provide more reproducibility, and adjustability.

SCRATCHY combines two methods for recombining genes, ITCHY and DNA shuffling (Lutz et al., Proc. Natl. Acad. Sci. USA 98:11248-11253 (2001)). SCRATCHY combines the best features of ITCHY and DNA shuffling. First, ITCHY is used to create a comprehensive set of fusions between fragments of genes in a DNA homology-independent fashion. This artificial family is then subjected to a DNA-shuffling step to augment the number of crossovers. Computational predictions can be used in optimization. SCRATCHY is more effective than DNA shuffling when sequence identity is below 80%.

In Random Drift Mutagenesis (RNDM) mutations made via epPCR followed by screening/selection for those retaining usable activity (Bergquist et al., Biomol. Eng. 22:63-72 (2005)). Then, these are used in DOGS to generate recombinants with fusions between multiple active mutants or between active mutants and some other desirable parent. Designed to promote isolation of neutral mutations; its purpose is to screen for retained catalytic activity whether or not this activity is higher or lower than in the original gene. RNDM is usable in high throughput assays when screening is capable of detecting activity above background. RNDM has been used as a front end to DOGS in generating diversity. The technique imposes a requirement for activity prior to shuffling or other subsequent steps; neutral drift libraries are indicated to result in higher/quicker improvements in activity from smaller libraries. Though published using epPCR, this could be applied to other large-scale mutagenesis methods.

Sequence Saturation Mutagenesis (SeSaM) is a random mutagenesis method that: 1) generates a pool of random length fragments using random incorporation of a phosphothioate nucleotide and cleavage; this pool is used as a template to 2) extend in the presence of “universal” bases such as inosine; 3) replication of an inosine-containing complement gives random base incorporation and, consequently, mutagenesis (Wong et al., Biotechnol. J. 3:74-82 (2008); Wong et al., Nucleic Acids Res. 32:e26 (2004); and Wong et al., Anal. Biochem. 341:187-189 (2005)). Using this technique it can be possible to generate a large library of mutants within 2 to 3 days using simple methods. This technique is non-directed in comparison to the mutational bias of DNA polymerases. Differences in this approach makes this technique complementary (or an alternative) to epPCR.

In Synthetic Shuffling, overlapping oligonucleotides are designed to encode “all genetic diversity in targets” and allow a very high diversity for the shuffled progeny (Ness et al., Nat. Biotechnol. 20:1251-1255 (2002)). In this technique, one can design the fragments to be shuffled. This aids in increasing the resulting diversity of the progeny. One can design sequence/codon biases to make more distantly related sequences recombine at rates approaching those observed with more closely related sequences. Additionally, the technique does not require physically possessing the template genes.

Nucleotide Exchange and Excision Technology NexT exploits a combination of dUTP incorporation followed by treatment with uracil DNA glycosylase and then piperidine to perform endpoint DNA fragmentation (Muller et al., Nucleic Acids Res. 33:e117 (2005)). The gene is reassembled using internal PCR primer extension with proofreading polymerase. The sizes for shuffling are directly controllable using varying dUPT::dTTP ratios. This is an end point reaction using simple methods for uracil incorporation and cleavage. Other nucleotide analogs, such as 8-oxo-guanine, can be used with this method. Additionally, the technique works well with very short fragments (86 bp) and has a low error rate. The chemical cleavage of DNA used in this technique results in very few unshuffled clones.

In Sequence Homology-Independent Protein Recombination (SHIPREC), a linker is used to facilitate fusion between two distantly related or unrelated genes. Nuclease treatment is used to generate a range of chimeras between the two genes. These fusions result in libraries of single-crossover hybrids (Sieber et al., Nat. Biotechnol. 19:456-460 (2001)). This produces a limited type of shuffling and a separate process is required for mutagenesis. In addition, since no homology is needed, this technique can create a library of chimeras with varying fractions of each of the two unrelated parent genes. SHIPREC was tested with a heme-binding domain of a bacterial CP450 fused to N-terminal regions of a mammalian CP450; this produced mammalian activity in a more soluble enzyme.

In Gene Site Saturation Mutagenesis™ (GSSM™) the starting materials are a supercoiled dsDNA plasmid containing an insert and two primers which are degenerate at the desired site of mutations (Kretz et al., Methods Enzymol. 388:3-11 (2004)). Primers carrying the mutation of interest, anneal to the same sequence on opposite strands of DNA. The mutation is typically in the middle of the primer and flanked on each side by approximately 20 nucleotides of correct sequence. The sequence in the primer is NNN or NNK (coding) and MNN (noncoding) (N=all 4, K=G, T, M=A, C). After extension, DpnI is used to digest dam-methylated DNA to eliminate the wild-type template. This technique explores all possible amino acid substitutions at a given locus (that is, one codon). The technique facilitates the generation of all possible replacements at a single-site with no nonsense codons and results in equal to near-equal representation of most possible alleles. This technique does not require prior knowledge of the structure, mechanism, or domains of the target enzyme. If followed by shuffling or Gene Reassembly, this technology creates a diverse library of recombinants containing all possible combinations of single-site up-mutations. The usefulness of this technology combination has been demonstrated for the successful evolution of over 50 different enzymes, and also for more than one property in a given enzyme.

Combinatorial Cassette Mutagenesis (CCM) involves the use of short oligonucleotide cassettes to replace limited regions with a large number of possible amino acid sequence alterations (Reidhaar-Olson et al. Methods Enzymol. 208:564-586 (1991); and Reidhaar-Olson et al. Science 241:53-57 (1988)). Simultaneous substitutions at two or three sites are possible using this technique. Additionally, the method tests a large multiplicity of possible sequence changes at a limited range of sites. This technique has been used to explore the information content of the lambda repressor DNA-binding domain.

Combinatorial Multiple Cassette Mutagenesis (CMCM) is essentially similar to CCM except it is employed as part of a larger program: 1) use of epPCR at high mutation rate to 2) identify hot spots and hot regions and then 3) extension by CMCM to cover a defined region of protein sequence space (Reetz et al., Angew. Chem. Int. Ed Engl. 40:3589-3591 (2001)). As with CCM, this method can test virtually all possible alterations over a target region. If used along with methods to create random mutations and shuffled genes, it provides an excellent means of generating diverse, shuffled proteins. This approach was successful in increasing, by 51-fold, the enantioselectivity of an enzyme.

In the Mutator Strains technique, conditional ts mutator plasmids allow increases of 20 to 4000-X in random and natural mutation frequency during selection and block accumulation of deleterious mutations when selection is not required (Selifonova et al., Appl. Environ. Microbiol. 67:3645-3649 (2001)). This technology is based on a plasmid-derived mutD5 gene, which encodes a mutant subunit of DNA polymerase III. This subunit binds to endogenous DNA polymerase III and compromises the proofreading ability of polymerase III in any strain that harbors the plasmid. A broad-spectrum of base substitutions and frameshift mutations occur. In order for effective use, the mutator plasmid should be removed once the desired phenotype is achieved; this is accomplished through a temperature sensitive (ts) origin of replication, which allows for plasmid curing at 41° C. It should be noted that mutator strains have been explored for quite some time (see Low et al., J. Mol. Biol. 260:359-3680 (1996)). In this technique, very high spontaneous mutation rates are observed. The conditional property minimizes non-desired background mutations. This technology could be combined with adaptive evolution to enhance mutagenesis rates and more rapidly achieve desired phenotypes.

Look-Through Mutagenesis (LTM) is a multidimensional mutagenesis method that assesses and optimizes combinatorial mutations of selected amino acids (Rajpal et al., Proc. Natl. Acad. Sci. USA 102:8466-8471 (2005)). Rather than saturating each site with all possible amino acid changes, a set of nine is chosen to cover the range of amino acid R-group chemistry. Fewer changes per site allows multiple sites to be subjected to this type of mutagenesis. A >800-fold increase in binding affinity for an antibody from low nanomolar to picomolar has been achieved through this method. This is a rational approach to minimize the number of random combinations and can increase the ability to find improved traits by greatly decreasing the numbers of clones to be screened. This has been applied to antibody engineering, specifically to increase the binding affinity and/or reduce dissociation. The technique can be combined with either screens or selections.

Gene Reassembly is a DNA shuffling method that can be applied to multiple genes at one time or to create a large library of chimeras (multiple mutations) of a single gene (Tunable GeneReassembly™ (TGR™) Technology supplied by Verenium Corporation). Typically this technology is used in combination with ultra-high-throughput screening to query the represented sequence space for desired improvements. This technique allows multiple gene recombination independent of homology. The exact number and position of cross-over events can be pre-determined using fragments designed via bioinformatic analysis. This technology leads to a very high level of diversity with virtually no parental gene reformation and a low level of inactive genes. Combined with GSSM™, a large range of mutations can be tested for improved activity. The method allows “blending” and “fine tuning” of DNA shuffling, for example, codon usage can be optimized.

In Silico Protein Design Automation (PDA) is an optimization algorithm that anchors the structurally defined protein backbone possessing a particular fold, and searches sequence space for amino acid substitutions that can stabilize the fold and overall protein energetics (Hayes et al., Proc. Natl. Acad. Sci. USA 99:15926-15931 (2002)). This technology uses in silico structure-based entropy predictions in order to search for structural tolerance toward protein amino acid variations. Statistical mechanics is applied to calculate coupling interactions at each position. Structural tolerance toward amino acid substitution is a measure of coupling. Ultimately, this technology is designed to yield desired modifications of protein properties while maintaining the integrity of structural characteristics. The method computationally assesses and allows filtering of a very large number of possible sequence variants (10⁵⁰). The choice of sequence variants to test is related to predictions based on the most favorable thermodynamics. Ostensibly only stability or properties that are linked to stability can be effectively addressed with this technology. The method has been successfully used in some therapeutic proteins, especially in engineering immunoglobulins. In silico predictions avoid testing extraordinarily large numbers of potential variants. Predictions based on existing three-dimensional structures are more likely to succeed than predictions based on hypothetical structures. This technology can readily predict and allow targeted screening of multiple simultaneous mutations, something not possible with purely experimental technologies due to exponential increases in numbers.

Iterative Saturation Mutagenesis (ISM) involves: 1) using knowledge of structure/function to choose a likely site for enzyme improvement; 2) performing saturation mutagenesis at chosen site using a mutagenesis method such as Stratagene QuikChange (Stratagene; San Diego Calif.); 3) screening/selecting for desired properties; and 4) using improved clone(s), start over at another site and continue repeating until a desired activity is achieved (Reetz et al., Nat. Protoc. 2:891-903 (2007); and Reetz et al., Angew. Chem. Int. Ed Engl. 45:7745-7751 (2006)). This is a proven methodology, which assures all possible replacements at a given position are made for screening/selection.

Any of the aforementioned methods for mutagenesis can be used alone or in any combination. Additionally, any one or combination of the directed evolution methods can be used in conjunction with adaptive evolution techniques, as described herein.

It is understood that modifications which do not substantially affect the activity of the various embodiments of this invention are also provided within the definition of the invention provided herein. Accordingly, the following examples are intended to illustrate but not limit the present invention.

Example I Pathways for Producing Propylene from 2-Ketoglutarate or Pyruvate

Disclosed herein are novel processes for the direct production of propylene using engineered non-natural microorganisms that possess the enzymes necessary for conversion of common metabolites into the three carbon alkene, propylene. Direct production of propylene entails use of the well-known ethylene forming enzyme (EFE), which has been isolated and characterized from, for example, pathovars of the plant pathogen Pseudomonas syringae and shown to convert 2-ketoglutarate into ethylene and carbon dioxide (FIG. 1). The EFE enzyme or a variant of EFE is used for conversion of 3-methyl-2-ketoglutarate or 4-methyl-2-ketoglutarate into propylene and carbon dioxide in a manner analogous to the conversion of 2-ketoglutarate (step 2 of FIG. 2 and step F of FIG. 3). Thus we refer this enzyme herein as propylene forming enzyme (PFE). The intermediate 3-methyl-2-ketoglutarate can be formed directly from 2-ketoglutarate through an S-adenosylmethionine-dependent methyltransferase enzyme such as that encoded by, for example, the gene glmT in Streptomyces frudiae and other organisms (step 1 of FIG. 2). Alternatively, it can be formed from leucine or acetoacetate and acetyl-CoA as depicted in FIG. 4. The intermediate 4-methyl-2-oxo-glutarate can be formed through aldolase-catalyzed transformation of pyruvate to 4-hydroxy-4-methyl-2-ketoglutarate, followed by dehydration with the enzyme or variant of malate dehydratase and subsequent reduction with an enoate reductase or with an enzyme or variant of fumarate reductase (steps A-E of FIG. 3). Alternatively, it can be formed from lysine depicted in FIG. 5. Enzyme candidates for steps 1 and 2 of FIG. 2 and steps A-F of FIG. 3 are provided below.

Step 1 of FIG. 2 depicts 2-ketoglutarate methyltransferase which catalyzes the methylation of 2-ketoglutarate to form 3-methyl-2-ketoglutarate. Such activity can be obtained using enzymes encoded by glmT from Streptomyces coelicolor, dptI from Streptomyces roseosporus, and lptI from Streptomyces fradiae (Mahlert et al., J. Am. Chem. Soc., 2007, 129 (39), 12011-12018).

GenBank GI Gene Accession No. Number Organism glmT NP_627429.1 21221650 Streptomyces coelicolor A3(2) dptI ZP_04706744.1 239986080 Streptomyces roseosporus NRRL 11379 lptI AAZ23087.1 71068232 Streptomyces fradiae

Several candidate genes are likely to naturally exhibit PFE activity on either 3-methyl-2-ketoglutarate (step 2, FIG. 2) or 4-methyl-2-ketoglutarate (step F, FIG. 3). If not, they can be engineered to exhibit PFE activity on these substrates. Candidate genes include EFEs from various strains of Pseudomonas syringae and Ralstonia solanacearum (Fukuda et al., Biochem Biophys Res Comm, 1992, 188 (2), 826-832; Tao et al., Appl Microbiol Biotechnol, 2008, 80(4):573-8; Chen et al., Int J of Biol Sci, 2010, 6(1):96-106; Weingart et al., Phytopathology, 1999, 89:360-365).

GenBank GI Gene Accession No. Number Organism Efe BAA02477.1 216878 Pseudomonas syringae pv. phaseolicola PK2 Efe AAD16443.1 4323603 Pseudomonas syringae pv. Pisi Efe Q7BS32.1 50897474 Pseudomonas syringae pv. glycinea Efe CAD18680.1 17432003 Ralstonia solanacearum

Step A of FIG. 3 depicts 4-hydroxy-4-methyl-2-ketoglutarate aldolase which catalyzes the condensation of two pyruvate molecules to form 4-hydroxy-4-methyl-2-ketoglutarate. Genes from the following organisms encoded enzymes that catalyze 4-hydroxy-4-methyl-2-ketoglutarate aldolase: Pseudomonas ochraceae NGJ1 (Maruyama et al., Biosci Biotechnol Biochem, 2001, 65(12):2701-2709), Pseudomonas putida (Dagley, Methods Enzymol, 1982, 90:272-276), and Pseudomonas testosteroni (or Comamonas testosteroni) (Providenti et al., Microbiology, 2001 147 (Pt 8), 2157-2167), and Arachis hypogaea.

GenBank GI Gene Accession No. Number Organism proA BAB21456.3 13094205 Pseudomonas ochraceae NGJ1 Pput_1361 ABQ77519.1 148510659 Pseudomonas putida F1 Pput_3204 ABQ79330.1 148512470 Pseudomonas putida F1 CtCNB1_2744 YP_003278786.1 264678879 Comamonas testosteroni

Step D of FIG. 3 depicts 4-hydroxy-4-methyl-2-ketoglutarate dehydratase I which dehydrates 4-hydroxy-4-methyl-2-ketoglutarate to form 4-methyl-2-ketoglutaconate. Step B of FIG. 3 depicts 4-hydroxy-4-methyl-2-ketoglutarate dehydratase II which dehydrates 4-hydroxy-4-methyl-2-ketoglutarate to form 4-methylene-2-ketoglutarate. Various classes of dehydratases can be applied to catalyze these transformations. Specific examples are provided below and several additional dehydratase enzymes in the EC 4.2.1 can be alternatively utilized.

For example, one enzyme that catalyzes a similar transformation is citramalate hydrolyase (EC 4.2.1.34), an enzyme that naturally dehydrates 2-methylmalate to mesaconate. This enzyme has been studied in Methanocaldococcus jannaschii in the context of the pyruvate pathway to 2-oxobutanoate, where it has been shown to have a broad substrate specificity (Drevland et al., J. Bacteriol. 189:4391-4400 (2007)). This enzyme activity was also detected in Clostridium tetanomorphum, Morganella morganii, Citrobacter amalonaticus where it is thought to participate in glutamate degradation (Kato and Asano Arch. Microbiol. 168:457-463 (1997)). The M. jannaschii protein sequence does not bear significant homology to genes in these organisms. Genbank information related to this gene is summarized below.

GenBank GI Gene Accession No. Number Organism leuD 3122345 Q58673.1 Methanocaldococcus jannaschii

Another useful enzyme is fumarate hydratase (EC 4.2.1.2), also known as fumarase, that catalyzes the reversible hydration of fumarate to malate. The three fumarases of E. coli, encoded by fumA, fumB and fumC, are regulated under different conditions of oxygen availability. FumB is oxygen sensitive and is active under anaerobic conditions. FumA is active under microanaerobic conditions, and FumC is active under aerobic growth conditions (Tseng et al., J. Bacteriol. 183:461-467 (2001);Woods et al., Biochim. Biophys. Acta 954:14-26 (1988); Guest et al., J. Gen. Microbiol. 131:2971-2984 (1985)). S. cerevisiae contains one copy of a fumarase-encoding gene, FUM1, whose product localizes to both the cytosol and mitochondrion (Sass et al., J. Biol. Chem. 278:45109-45116 (2003)). Additional fumarase enzymes are found in Campylobacter jejuni (Smith et al., Int. J. Biochem. Cell. Biol. 31:961-975 (1999)), Thermus thermophilus (Mizobata et al., Arch. Biochem. Biophys. 355:49-55 (1998)) and Rattus norvegicus (Kobayashi et al., J. Biochem. 89:1923-1931 (1981)). Similar enzymes with high sequence homology include fum1 from Arabidopsis thaliana and fumC from Corynebacterium glutamicum. The MmcBC fumarase from Pelotomaculum thermopropionicum is another class of fumarase with two subunits (Shimoyama et al., FEMS Microbiol. Lett. 270:207-213 (2007)). Genbank information related to these genes is summarized below.

GenBank GI Gene Accession No. Number Organism fumA NP_416129.1 16129570 Escherichia coli fumB NP_418546.1 16131948 Escherichia coli fumC NP_416128.1 16129569 Escherichia coli FUM1 NP_015061 6324993 Saccharomyces cerevisiae fumC Q8NRN8.1 39931596 Corynebacterium glutamicum fumC O69294.1 9789756 Campylobacter jejuni fumC P84127 75427690 Thermus thermophilus fumH P14408.1 120605 Rattus norvegicus MmcB YP_001211906 147677691 Pelotomaculum thermopropionicum MmcC YP_001211907 147677692 Pelotomaculum thermopropionicum

The enzyme OHED hydratase participates in 4-hydroxyphenylacetic acid degradation, where it converts 2-oxo-hept-4-ene-1,7-dioate (OHED) to 2-oxo-4-hydroxy-hepta-1,7-dioate (HODH) using magnesium as a cofactor (Burks et al., J. Am. Chem. Soc.120 (1998). OHED hydratase enzymes have been identified and characterized in E. coli C (Izumi et la., J. Mol. Biol. 370:899-911 (2007); Roper et al., Gene 156:47-51 (1995)) and E. coli W (Prieto et al., J. Bacteriol. 178:111-120 (1996)). Sequence comparison reveals homologs in a range of bacteria, plants and animals. Enzymes with highly similar sequences are contained in Klebsiella pneumonia (91% identity, evalue=2e-138) and Salmonella enterica (91% identity, evalue=4e-138), among others. Genbank information related to these genes is summarized below.

GenBank GI Gene Accession No. Number Organism hpcG CAA57202.1 556840 Escherichia coli C hpaH CAA86044.1 757830 Escherichia coli W hpaH ABR80130.1 150958100 Klebsiella pneumoniae Sari_01896 ABX21779.1 160865156 Salmonella enterica

Yet another enzyme catalyzing a dehydration similar to step D of FIG. 3 is 2-(hydroxymethyl)glutarate dehydratase of Eubacterium barkeri. This enzyme has been studied in the context of nicotinate catabolism and is encoded by hmd (Alhapel et al., Proc. Natl. Acad. Sci. USA 103:12341-12346 (2006)). Similar enzymes with high sequence homology are found in Bacteroides capillosus and Anaerotruncus colihominis. These enzymes are also homologous to the α- and β-subunits of [4Fe-4S]-containing bacterial serine dehydratases, for example, E. coli enzymes encoded by tdcG, sdhB, and sdaA). Genbank information related to these genes is summarized below.

GenBank GI Gene Accession No. Number Organism hmd ABC88407.1 86278275 Eubacterium barkeri BACCAP_02294 ZP_02036683.1 154498305 Bacteroides capillosus ATCC 29799 ANACOL_02527 ZP_02443222.1 167771169 Anaerotruncus colihominis DSM 17241

Another gene capable of encoding a dehydratase enzyme for step B or step D of FIG. 3 is 4-oxalomesaconate hydratase (or 4-carboxy-4-hydroxy-2-ketoadipate dehydratase). Exemplary enzymes can be found in Comamonas testosteroni (Providenti et al., Microbiology, 2001, 147(Pt 8);2157-67), Sphingomonas sp. SYK6 (Hara, et al., J Bacteriol, 2000, 182(24);6950-7), and Pseudomonas ochraceae NGJ1 (Maruyama et al., Biosci Biotechnol Biochem, 2001 65(12);2701-9; Maruyama et al., Biosci Biotechnol Biochem, 2004, 68(7);1434-41).

GenBank GI Gene Accession No. Number Organism pmdE YP_003278787.1 264678880 Comamonas testosteroni ligJ BAA97116.1 8777583 Sphingomonas sp. SYK6 proH BAB21455.1 12539404 Pseudomonas ochraceae NGJ1

Step C of FIG. 3 depicts 4-methylene-2-ketoglutarate reductase which reduces 4-methylene-2-ketoglutarate reductase to form 4-methyl-2-ketoglutarate. Step E of FIG. 3 depicts 4-methyl-2-ketoglutaconate reductase which reduces 4-methyl-2-ketoglutaconate to form 4-methyl-2-ketoglutarate. Various classes of enoate reductases can be applied to catalyze these transformations. Specific examples are provided below and several additional enoate reductase enzymes in the EC 1.3.1 can be alternatively utilized.

2-Enoate oxidoreductase enzymes are known to catalyze the NAD(P)H-dependent reduction and oxidation of a wide variety of α,β-unsaturated carboxylic acids and aldehydes (Rohdich et al., J. Biol. Chem. 276:5779-5787 (2001)). In the recently published genome sequence of C. kluyveri, 9 coding sequences for enoate reductases were reported, out of which one has been characterized (Seedorf et al., Proc. Natl. Acad. Sci. U.S.A. 105:2128-2133 (2008)). The enr genes from both C. tyrobutyricum and M. thermoaceticum have been cloned and sequenced and show 59% identity to each other. The former gene is also found to have approximately 75% similarity to the characterized gene in C. kluyveri (Giesel and Simon, Arch. Microbiol. 135:51-57 (1983)). It has been reported based on these sequence results that enr is very similar to the dienoyl CoA reductase in E. coli (fadH) (Rohdich et al., J. Biol. Chem. 276:5779-5787 (2001)). The C. thermoaceticum enr gene has also been expressed in a catalytically active form in E. coli (Rohdich et al., supra). Genbank information related to these genes is summarized below.

GenBank GI Gene Accession No. Number Organism enr ACA54153.1 169405742 Clostridium botulinum A3 str enr CAA71086.1 2765041 Clostridium tyrobutyricum enr CAA76083.1 3402834 Clostridium kluyveri enr YP_430895.1 83590886 Moorella thermoacetica fadH NP_417552.1 16130976 Escherichia coli

MAR is a 2-enoate oxidoreductase catalyzing the reversible reduction of 2-maleylacetate (cis-4-oxohex-2-enedioate) to 3-oxoadipate (FIG. 2, Step O). MAR enzymes naturally participate in aromatic degradation pathways (Camara et al., J. Bacteriol. 191:4905-4915 (2009); Huang et al., Appl. Environ. Microbiol. 72:7238-7245 (2006); Kaschabek and Reineke, J. Bacteriol. 177:320-325 (1995); Kaschabek and Reineke, J. Bacteriol. 175:6075-6081 (1993)). The enzyme activity was identified and characterized in Pseudomonas sp. strain B13 (Kaschabek and Reineke, (1995) supra; Kaschabek and Reineke, (1993) supra), and the coding gene was cloned and sequenced (Kasberg et al., J. Bacteriol. 179:3801-3803 (1997)). Additional MAR genes include cicE gene from Pseudomonas sp. strain B13 (Kasberg et al., supra), macA gene from Rhodococcus opacus (Seibert et al., J. Bacteriol. 175:6745-6754 (1993)), the macA gene from Ralstonia eutropha (also known as Cupriavidus necator) (Seibert et al., Microbiology 150:463-472 (2004)), tfdFII from Ralstonia eutropha (Seibert et al., (1993) supra) and NCgl1112 in Corynebacterium glutamicum (Huang et al., Appl. Environ Microbiol. 72:7238-7245 (2006)). A MAR in Pseudomonas reinekei MT1, encoded by ccaD, was recently identified and the nucleotide sequence is available under the DBJ/EMBL GenBank accession number EF159980 (Camara et al., J. Bacteriol. 191:4905-4915 (2009). Genbank information related to these genes is summarized below.

GenBank GI Gene Accession No. Number Organism clcE O30847.1 3913241 Pseudomonas sp. strain B13 macA O84992.1 7387876 Rhodococcus opacus macA AAD55886 5916089 Cupriavidus necator tfdFII AC44727.1 1747424 Ralstonia eutropha JMP134 NCgl1112 NP_600385 19552383 Corynebacterium glutamicum ccaD EF159980.1 134133935 Pseudomonas reinekei MT1

Fumarate reductase catalyzes the reduction of fumarate to succinate. The fumarate reductase of E. coli, composed of four subunits encoded by frdABCD, is membrane-bound and active under anaerobic conditions. The electron donor for this reaction is menaquinone and the two protons produced in this reaction do not contribute to the proton gradient (Iverson et al., Science 284:1961-1966 (1999)). The yeast genome encodes two soluble fumarate reductase isozymes encoded by FRDS1 (Enomoto et al., DNA Res. 3:263-267 (1996)) and FRDS2 (Muratsubaki et al., Arch. Biochem. Biophys. 352:175-181 (1998)), which localize to the cytosol and promitochondrion, respectively, and are used for anaerobic growth on glucose (Arikawa et al., FEMS Microbiol. Lett. 165:111-116 (1998)).

GenBank GI Protein Accession No. Number Organism FRDS1 P32614 418423 Saccharomyces cerevisiae FRDS2 NP_012585 6322511 Saccharomyces cerevisiae frdA NP_418578.1 16131979 Escherichia coli frdB NP_418577.1 16131978 Escherichia coli frdC NP_418576.1 16131977 Escherichia coli frdD NP_418475.1 16131877 Escherichia coli

Throughout this application various publications have been referenced. The disclosures of these publications in their entireties, including GenBank and GI number publications, are hereby incorporated by reference in this application in order to more fully describe the state of the art to which this invention pertains. Although the invention has been described with reference to the examples provided above, it should be understood that various modifications can be made without departing from the spirit of the invention. 

1. A non-naturally occurring microbial organism, comprising a microbial organism having a propylene pathway comprising at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce propylene, said propylene pathway comprising a propylene forming enzyme or a 2-ketoglutarate methyltransferase.
 2. The non-naturally occurring microbial organism of claim 1, wherein said microbial organism comprises two exogenous nucleic acids each encoding a propylene pathway enzyme.
 3. The non-naturally occurring microbial organism of claim 1, wherein said propylene pathway comprises a 2-ketoglutarate methyltransferase and a propylene forming enzyme.
 4. The non-naturally occurring microbial organism of claim 1, wherein said at least one exogenous nucleic acid is a heterologous nucleic acid.
 5. The non-naturally occurring microbial organism of claim 1, wherein said non-naturally occurring microbial organism is in a substantially anaerobic culture medium.
 6. A non-naturally occurring microbial organism, comprising a microbial organism having a propylene pathway comprising at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce propylene, said propylene pathway comprising a propylene forming enzyme, a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase II, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase I, a 4-methylene-2-ketoglutarate reductase, or a 4-methyl-2-ketoglutaconate reductase.
 7. The non-naturally occurring microbial organism of claim 6, wherein said microbial organism comprises two exogenous nucleic acids each encoding a propylene pathway enzyme.
 8. The non-naturally occurring microbial organism of claim 6, wherein said microbial organism comprises three exogenous nucleic acids each encoding a propylene pathway enzyme.
 9. The non-naturally occurring microbial organism of claim 6, wherein said microbial organism comprises four exogenous nucleic acids each encoding a propylene pathway enzyme.
 10. The non-naturally occurring microbial organism of claim 6, wherein said propylene pathway comprises a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase II, a 4-methylene-2-ketoglutarate reductase and a propylene forming enzyme.
 11. The non-naturally occurring microbial organism of claim 6, wherein said propylene pathway comprises a 4-hydroxy-4-methyl-2-ketoglutarate aldolase, a 4-hydroxy-4-methyl-2-ketoglutarate dehydratase I, a 4-methyl-2-ketoglutaconate reductase and a propylene forming enzyme.
 12. The non-naturally occurring microbial organism of claim 6, wherein said at least one exogenous nucleic acid is a heterologous nucleic acid.
 13. The non-naturally occurring microbial organism of claim 6, wherein said non-naturally occurring microbial organism is in a substantially anaerobic culture medium.
 14. A method for producing propylene, comprising culturing the non-naturally occurring microbial organism of claim 1 under conditions and for a sufficient period of time to produce propylene.
 15. The method of claim 14, wherein said non-naturally occurring microbial organism is in a substantially anaerobic culture medium.
 16. A method for producing propylene, comprising culturing the non-naturally occurring microbial organism of claims 6 under conditions and for a sufficient period of time to produce propylene.
 17. The method of claim 16, wherein said non-naturally occurring microbial organism is in a substantially anaerobic culture medium. 